Programs & Examples On #Sizzle

Sizzle is a JavaScript CSS selector engine.

Wildcards in jQuery selectors

for classes you can use:


How to break nested loops in JavaScript?

    for (var i in set1) {
        for (var j in set2) {
            for (var k in set3) {
                break loop2;  // breaks out of loop3 and loop2

code copied from Best way to break from nested loops in Javascript?

Please search before posting a question. The link was the FIRST related question I saw on the left side of this page!

JSF rendered multiple combined conditions

Assuming that "a" and "b" are bean properties

rendered="#{bean.a==12 and (bean.b==13 or bean.b==15)}"

You may look at JSF EL operators

Use sudo with password as parameter

You can set the s bit for your script so that it does not need sudo and runs as root (and you do not need to write your root password in the script):

sudo chmod +s myscript

ASP.NET IIS Web.config [Internal Server Error]

I experienced the same issue, and found out that the applicationdeployed was of .NET version 3.5, but the Application pool was using .NET 2.0. That caused the problem you described above. Hope it helps someone.

My error:

HTTP Error 500.19 - Internal Server Error
The requested page cannot be accessed because the related configuration data for the page is invalid. Detailed Error Information
Module IIS Web Core 
Notification BeginRequest 
Handler Not yet determined 
Error Code 0x80070021 

Config Error This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false".  
Config File \\?\C:\inetpub\MyService\web.config 
Requested URL http://localhost:80/MyService.svc 
Physical Path C:\inetpub\DeployService\DeployService.svc 
Logon Method Not yet determined 
Logon User Not yet determined 
 Config Source
101:        </modules>
  102:      <handlers>
  103:          <remove name="WebServiceHandlerFactory-Integrated"/>
HTTP Error 500.19 - Internal Server Error
The requested page cannot be accessed because the related configuration data for the page is invalid. Detailed Error Information
Module IIS Web Core 
Notification BeginRequest 
Handler Not yet determined 
Error Code 0x80070021 
Config Error This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false".  

Config File \\?\C:\inetpub\DeployService\web.config 
Requested URL http://localhost:80/DeployService.svc 
Physical Path C:\inetpub\DeployService\DeployService.svc 
Logon Method Not yet determined 
Logon User Not yet determined 
 Config Source
  101:      </modules>
  102:      <handlers>
  103:          <remove name="WebServiceHandlerFactory-Integrated"/>`

Convert object to JSON in Android

As of Android 3.0 (API Level 11) Android has a more recent and improved JSON Parser.

Reads a JSON (RFC 4627) encoded value as a stream of tokens. This stream includes both literal values (strings, numbers, booleans, and nulls) as well as the begin and end delimiters of objects and arrays. The tokens are traversed in depth-first order, the same order that they appear in the JSON document. Within JSON objects, name/value pairs are represented by a single token.

How does the JPA @SequenceGenerator annotation work

I have MySQL schema with autogen values. I use strategy=GenerationType.IDENTITY tag and seems to work fine in MySQL I guess it should work most db engines as well.

    id bigint NOT NULL auto_increment,
    name varchar(64) NOT NULL default '',
    PRIMARY KEY (id)

// mark this JavaBean to be JPA scoped class
public class User {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private long id;    // primary key (autogen surrogate)

    private String name;

    public long getId() { return id; }
    public void setId(long id) { = id; }

    public String getName() { return name; }
    public void setName(String name) {; }

Iterate through pairs of items in a Python list

>>> a = [5, 7, 11, 4, 5]
>>> for n,k in enumerate(a[:-1]):
...     print a[n],a[n+1]
5 7
7 11
11 4
4 5

How can I override Bootstrap CSS styles?

A bit late but what I did is I added a class to the root div then extends every bootstrap elements in my custom stylesheet:

.overrides .list-group-item {
    border-radius: 0px;
.overrides .some-elements-from-bootstrap { 
    /* styles here */
<div class="container-fluid overrides">
    <div class="row">
        <div class="col-sm-4" style="background-color: red">
            <ul class="list-group">
                <li class="list-group-item"><a href="#">Hey</a></li>
                <li class="list-group-item"><a href="#">I was doing</a></li>
                <li class="list-group-item"><a href="#">Just fine</a></li>
                <li class="list-group-item"><a href="#">Until I met you</a></li>
                <li class="list-group-item"><a href="#">I drink too much</a></li>
                <li class="list-group-item"><a href="#">And that's an issue</a></li>
                <li class="list-group-item"><a href="#">But I'm okay</a></li>
        <div class="col-sm-8" style="background-color: blue">

Angular directives - when and how to use compile, controller, pre-link and post-link

What else happens between these function calls?

The various directive functions are executed from within two other angular functions called $compile (where the directive's compile is executed) and an internal function called nodeLinkFn (where the directive's controller, preLink and postLink are executed). Various things happen within the angular function before and after the directive functions are called. Perhaps most notably is the child recursion. The following simplified illustration shows key steps within the compile and link phases:

An illustration showing Angular compile and link phases

To demonstrate the these steps, let's use the following HTML markup:

<div ng-repeat="i in [0,1,2]">
        <div>Inner content</div>

With the following directive:

myApp.directive( 'myElement', function() {
    return {
        restrict:   'EA',
        transclude: true,
        template:   '<div>{{label}}<div ng-transclude></div></div>'


The compile API looks like so:

compile: function compile( tElement, tAttributes ) { ... }

Often the parameters are prefixed with t to signify the elements and attributes provided are those of the source template, rather than that of the instance.

Prior to the call to compile transcluded content (if any) is removed, and the template is applied to the markup. Thus, the element provided to the compile function will look like so:

        <div ng-transclude></div>

Notice that the transcluded content is not re-inserted at this point.

Following the call to the directive's .compile, Angular will traverse all child elements, including those that may have just been introduced by the directive (the template elements, for instance).

Instance creation

In our case, three instances of the source template above will be created (by ng-repeat). Thus, the following sequence will execute three times, once per instance.


The controller API involves:

controller: function( $scope, $element, $attrs, $transclude ) { ... }

Entering the link phase, the link function returned via $compile is now provided with a scope.

First, the link function create a child scope (scope: true) or an isolated scope (scope: {...}) if requested.

The controller is then executed, provided with the scope of the instance element.


The pre-link API looks like so:

function preLink( scope, element, attributes, controller ) { ... }

Virtually nothing happens between the call to the directive's .controller and the .preLink function. Angular still provide recommendation as to how each should be used.

Following the .preLink call, the link function will traverse each child element - calling the correct link function and attaching to it the current scope (which serves as the parent scope for child elements).


The post-link API is similar to that of the pre-link function:

function postLink( scope, element, attributes, controller ) { ... }

Perhaps worth noticing that once a directive's .postLink function is called, the link process of all its children elements has completed, including all the children's .postLink functions.

This means that by the time .postLink is called, the children are 'live' are ready. This includes:

  • data binding
  • transclusion applied
  • scope attached

The template at this stage will thus look like so:

    <div class="ng-binding">
        <div ng-transclude>                
            <div class="ng-scope">Inner content</div>

What are some alternatives to ReSharper?

CodeRush. Also, Scott Hanselman has a nice post comparing them, ReSharper vs. CodeRush.

A more up-to-date comparison is in Coderush vs Resharper by Jason Irwin.

How to set focus to a button widget programmatically?

Try this:


Visual Studio Code pylint: Unable to import 'protorpc'

First I will check the python3 path where it lives

enter image description here

And then in the VS Code settings just add that path, for example:

"python.pythonPath": "/usr/local/bin/python3"

How do I find the stack trace in Visual Studio?

Do you mean finding a stack trace of the thrown exception location? That's either Debug/Exceptions, or better - Ctrl-Alt-E. Set filters for the exceptions you want to break on.

There's even a way to reconstruct the thrower stack after the exception was caught, but it's really unpleasant. Much, much easier to set a break on the throw.

How do you check if a selector matches something in jQuery?

I think most of the people replying here didn't quite understand the question, or else I might be mistaken.

The question is "how to check whether or not a selector exists in jQuery."

Most people have taken this for "how to check whether an element exists in the DOM using jQuery." Hardly interchangeable.

jQuery allows you to create custom selectors, but see here what happens when you try to use on e before initializing it;

"Syntax error, unrecognized expression: YEAH"

After running into this, I realized it was simply a matter of checking

if ($.expr[':']['YEAH']) {
    // Query for your :YEAH selector with ease of mind.


Array of char* should end at '\0' or "\0"?

The termination of an array of characters with a null character is just a convention that is specifically for strings in C. You are dealing with something completely different -- an array of character pointers -- so it really has no relation to the convention for C strings. Sure, you could choose to terminate it with a null pointer; that perhaps could be your convention for arrays of pointers. There are other ways to do it. You can't ask people how it "should" work, because you're assuming some convention that isn't there.

Visual Studio 2008 Product Key in Registry?

For 32 bit Windows:

Visual Studio 2003:


Visual Studio 2005:


Visual Studio 2008:


For 64 bit Windows:

Visual Studio 2003:


Visual Studio 2005:


Visual Studio 2008:



  • Data is a GUID without dashes. Put a dash ( – ) after every 5 characters to convert to product key.
  • If PIDKEY value is empty try to look at the subfolders e.g.




Find duplicate records in a table using SQL Server

Select EventID,count() as cnt from dbo.EventInstances group by EventID having count() > 1

How do you create a dropdownlist from an enum in ASP.NET MVC?

The best solution I found for this was combining this blog with Simon Goldstone's answer.

This allows use of the enum in the model. Essentially the idea is to use an integer property as well as the enum, and emulate the integer property.

Then use the [System.ComponentModel.Description] attribute for annotating the model with your display text, and use an "EnumDropDownListFor" extension in your view.

This makes both the view and model very readable and maintainable.


public enum YesPartialNoEnum
    [Description("Still undecided")]


[Display(Name = "The label for my dropdown list")]
public virtual Nullable<YesPartialNoEnum> CuriousQuestion{ get; set; }
public virtual Nullable<int> CuriousQuestionId
    get { return (Nullable<int>)CuriousQuestion; }
    set { CuriousQuestion = (Nullable<YesPartialNoEnum>)value; }


@using MyProject.Extensions
    @Html.EnumDropDownListFor(model => model.CuriousQuestion)

Extension (directly from Simon Goldstone's answer, included here for completeness):

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.ComponentModel;
using System.Reflection;
using System.Linq.Expressions;
using System.Web.Mvc.Html;

namespace MyProject.Extensions
    //Extension methods must be defined in a static class
    public static class MvcExtensions
        private static Type GetNonNullableModelType(ModelMetadata modelMetadata)
            Type realModelType = modelMetadata.ModelType;

            Type underlyingType = Nullable.GetUnderlyingType(realModelType);
            if (underlyingType != null)
                realModelType = underlyingType;
            return realModelType;

        private static readonly SelectListItem[] SingleEmptyItem = new[] { new SelectListItem { Text = "", Value = "" } };

        public static string GetEnumDescription<TEnum>(TEnum value)
            FieldInfo fi = value.GetType().GetField(value.ToString());

            DescriptionAttribute[] attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);

            if ((attributes != null) && (attributes.Length > 0))
                return attributes[0].Description;
                return value.ToString();

        public static MvcHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TEnum>> expression)
            return EnumDropDownListFor(htmlHelper, expression, null);

        public static MvcHtmlString EnumDropDownListFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TEnum>> expression, object htmlAttributes)
            ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
            Type enumType = GetNonNullableModelType(metadata);
            IEnumerable<TEnum> values = Enum.GetValues(enumType).Cast<TEnum>();

            IEnumerable<SelectListItem> items = from value in values
                                                select new SelectListItem
                                                    Text = GetEnumDescription(value),
                                                    Value = value.ToString(),
                                                    Selected = value.Equals(metadata.Model)

            // If the enum is nullable, add an 'empty' item to the collection
            if (metadata.IsNullableValueType)
                items = SingleEmptyItem.Concat(items);

            return htmlHelper.DropDownListFor(expression, items, htmlAttributes);

AttributeError: 'str' object has no attribute 'append'

Why myList[1] is considered a 'str' object?

Because it is a string. What else is 'from form', if not a string? (Actually, strings are sequences too, i.e. they can be indexed, sliced, iterated, etc. as well - but that's part of the str class and doesn't make it a list or something).

mList[1] returns the first item in the list 'from form'

If you mean that myList is 'from form', no it's not!!! The second (indexing starts at 0) element is 'from form'. That's a BIG difference. It's the difference between a house and a person.

Also, myList doesn't have to be a list from your short code sample - it could be anything that accepts 1 as index - a dict with 1 as index, a list, a tuple, most other sequences, etc. But that's irrelevant.

but I cannot append to item 1 in the list myList

Of course not, because it's a string and you can't append to string. String are immutable. You can concatenate (as in, "there's a new object that consists of these two") strings. But you cannot append (as in, "this specific object now has this at the end") to them.

Convert output of MySQL query to utf8


When using the MySQL client library, then you should prevent a conversion back to your connection's default charset. (see mysql_set_character_set()[1])

In this case, use an additional cast to binary:

SELECT column1, CAST(CONVERT(column2 USING utf8) AS binary)
FROM my_table
WHERE my_condition;

Otherwise, the SELECT statement converts to utf-8, but your client library converts it back to a (potentially different) default connection charset.

In MySQL, can I copy one row to insert into the same table?

This can be achieved with some creativity:

SET @sql = CONCAT('INSERT INTO <table> SELECT null, 
    FROM information_schema.columns 
    WHERE table_schema = '<database>' 
    AND table_name = '<table>' 
    AND column_name NOT IN ('id')), ' 
from <table> WHERE id = <id>');  

PREPARE stmt1 FROM @sql;
EXECUTE stmt1;

This will result in the new row getting an auto incremented id instead of the id from the selected row.

What is the best way to dump entire objects to a log in C#?

Following is another version that does the same thing (and handle nested properties), which I think is simpler (no dependencies on external libraries and can be modified easily to do things other than logging):

public class ObjectDumper
    public static string Dump(object obj)
        return new ObjectDumper().DumpObject(obj);

    StringBuilder _dumpBuilder = new StringBuilder();

    string DumpObject(object obj)
        DumpObject(obj, 0);
        return _dumpBuilder.ToString();

    void DumpObject(object obj, int nestingLevel = 0)
        var nestingSpaces = "".PadLeft(nestingLevel * 4);

        if (obj == null)
            _dumpBuilder.AppendFormat("{0}null\n", nestingSpaces);
        else if (obj is string || obj.GetType().IsPrimitive)
            _dumpBuilder.AppendFormat("{0}{1}\n", nestingSpaces, obj);
        else if (ImplementsDictionary(obj.GetType()))
            using (var e = ((dynamic)obj).GetEnumerator())
                var enumerator = (IEnumerator)e;
                while (enumerator.MoveNext())
                    dynamic p = enumerator.Current;

                    var key = p.Key;
                    var value = p.Value;
                    _dumpBuilder.AppendFormat("{0}{1} ({2})\n", nestingSpaces, key, value != null ? value.GetType().ToString() : "<null>");
                    DumpObject(value, nestingLevel + 1);
        else if (obj is IEnumerable)
            foreach (dynamic p in obj as IEnumerable)
                DumpObject(p, nestingLevel);
            foreach (PropertyDescriptor descriptor in TypeDescriptor.GetProperties(obj))
                string name = descriptor.Name;
                object value = descriptor.GetValue(obj);

                _dumpBuilder.AppendFormat("{0}{1} ({2})\n", nestingSpaces, name, value != null ? value.GetType().ToString() : "<null>");
                DumpObject(value, nestingLevel + 1);

    bool ImplementsDictionary(Type t)
        return t.GetInterfaces().Any(i => i.Name.Contains("IDictionary"));

The thread has exited with code 0 (0x0) with no unhandled exception

Well, an application may have a lot of threads running in parallel. Some are run by you, the coder, some are run by framework classes (espacially if you are in a GUI environnement).

When a thread has finished its task, it exits and stops to exist. There ie nothing alarming in this and you should not care.

Trigger a Travis-CI rebuild without pushing a commit?

Please make sure to Log In to Travis first. The rebuild button doesn't appear until you're logged in. I know this is obvious, but someone just tripped on it as well ;-)

Reordering arrays

Change 2 to 1 as the first parameter in the splice call when removing the element:

var tmp = playlist.splice(1, 1);
playlist.splice(2, 0, tmp[0]);

How do I set a conditional breakpoint in gdb, when char* x points to a string whose value equals "hello"?

You can use strcmp:

break x:20 if strcmp(y, "hello") == 0

20 is line number, x can be any filename and y can be any variable.

How to use select/option/NgFor on an array of objects in Angular2

I'm no expert with DOM or Javascript/Typescript but I think that the DOM-Tags can't handle real javascript object somehow. But putting the whole object in as a string and parsing it back to an Object/JSON worked for me:

interface TestObject {

  selector: 'app',
  template: `
      <h4>Select Object via 2-way binding</h4>

      <select [ngModel]="selectedObject | json" (ngModelChange)="updateSelectedValue($event)">
        <option *ngFor="#o of objArray" [value]="o | json" >{{}}</option>

      <h4>You selected:</h4> {{selectedObject }}
  directives: [FORM_DIRECTIVES]
export class App {
    this.objArray = [{name: 'foo', value: 1}, {name: 'bar', value: 1}];
    this.selectedObject = this.objArray[1];
  updateSelectedValue(event:string): void{
    this.selectedObject = JSON.parse(event);

How do I set up IntelliJ IDEA for Android applications?

The 5th step in "New Project' has apparently changed slightly since.

Where it says android sdk then has the drop down menu that says none, there is no longer a 'new' button.

  • 5.)

    • a.)click the ... to the right of none.
    • b.)click the + in the top left of new window dialog. (Add new Sdk)
    • c.)click android sdk from drop down menu
    • d.)select home directory for your android sdk
    • e.)select java sdk version you want to use
    • f.)select android build target.
    • g.)hit ok!

Javascript to stop HTML5 video playback on modal window close

I'm not sure whether ZohoGorganzola's solution is correct; however, you may want to try getting at the element directly rather than trying to invoke a method on the jQuery collection, so instead of




How to completely DISABLE any MOUSE CLICK

You can overlay a big, semi-transparent <div> that takes all the clicks. Just append a new <div> to <body> with this style:

.overlay {
    background-color: rgba(1, 1, 1, 0.7);
    bottom: 0;
    left: 0;
    position: fixed;
    right: 0;
    top: 0;

Notification not showing in Oreo

I have faced the problem but found a unique solution.
for me this was the old code

String NOTIFICATION_CHANNEL_ID = "com.codedevtech.emplitrack";

and the working code is

String NOTIFICATION_CHANNEL_ID = "emplitrack_channel";

may be the channel id should not contain dot '.'

"Agreeing to the Xcode/iOS license requires admin privileges, please re-run as root via sudo." when using GCC

sudo xcodebuild -license

will take care of it with no trouble on the command line. Note that you'll have to manually scroll through the license, and agree to its terms at the end, unless you add "accept" to the command line :

sudo xcodebuild -license accept

How to style a div to be a responsive square?

This is what I came up with. Here is a fiddle.

First, I need three wrapper elements for both a square shape and centered text.

<div><div><div>Lorem ipsum dolor sit amet, consectetuer adipiscing elit,
sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat

This is the stylecheet. It makes use of two techniques, one for square shapes and one for centered text.

body > div {
    width:50%; padding-bottom:50%;

body > div > div {
    position:absolute; top:0;
    height:100%; width:100%;
    border:1px solid #000;

body > div > div > div{
    vertical-align:middle; text-align:center;

How to convert a char array back to a string?

 //Given Character Array 
  char[] a = {'h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd'};

    //Converting Character Array to String using String funtion     
    //OUTPUT : hello world

Converting any given Array type to String using Java 8 Stream function

String stringValue = char[][]{a}).map(String::valueOf).collect(Collectors.joining());

jQuery: how to trigger anchor link's click event

It worked for me:

     window.location = $('#myanchor').attr('href');

How to set column header text for specific column in Datagridview C#

For info, if you are binding to a class, you can do this in your type via DisplayNameAttribute:

[DisplayName("Access key")]
public string AccessKey { get {...} set {...} }

Now the header-text on auto-generated columns will be "Access key".

Add Favicon to Website

  1. This is not done in PHP. It's part of the <head> tags in a HTML page.
  2. That icon is called a favicon. According to Wikipedia:

    A favicon (short for favorites icon), also known as a shortcut icon, website icon, URL icon, or bookmark icon is a 16×16 or 32×32 pixel square icon associated with a particular website or webpage.

  3. Adding it is easy. Just add an .ico image file that is either 16x16 pixels or 32x32 pixels. Then, in the web pages, add <link rel="shortcut icon" href="favicon.ico" type="image/x-icon"> to the <head> element.
  4. You can easily generate favicons here.

Activity restart on rotation Android

There are multiple ways to do this:

Handle orientation changes by yourself

Another alternative is to handle the orientation changes by yourself. But this is not considered a good practice.

Add this to your manifest file.


for Android 3.2 and later:


public void onConfigurationChanged(Configuration config) {

if (newConfig.orientation == Configuration.ORIENTATION_PORTRAIT) {
        //Handle rotation from landscape to portarit mode here
    } else if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE){
        //Handle rotation from portrait to landscape mode here

OR Restrict rotation

You can also confine your activity to portrait or landscape mode to avoid rotation.

Add this to the activity tag in your manifest file:


Or implement this programmatically in your activity:

    protected void onCreate(Bundle savedInstanceState) {

OR Save Activity State

You can save the activity state in onSaveInstanceState.

public void onSaveInstanceState(Bundle outState) {
    /*Save your data to be restored here
    Example : outState.putLong("time_state", time); , time is a long variable*/

and then use the bundle to restore the state.

protected void onCreate(Bundle savedInstanceState) {

    if(savedInstanceState!= null){
       /*When rotation occurs
        Example : time = savedInstanceState.getLong("time_state", 0); */
    } else {
      //When onCreate is called for the first time

Detecting the onload event of a window opened with

If the pop-up's document is from a different domain, this is simply not possible.

Update April 2015: I was wrong about this: if you own both domains, you can use window.postMessage and the message event in pretty much all browsers that are relevant today.

If not, there's still no way you'll be able to make this work cross-browser without some help from the document being loaded into the pop-up. You need to be able to detect a change in the pop-up that occurs once it has loaded, which could be a variable that JavaScript in the pop-up page sets when it handles its own load event, or if you have some control of it you could add a call to a function in the opener.

Using LIKE in an Oracle IN clause

You don't need a collection type as mentioned in Just use an subquery:

FROM tbl t
    SELECT 1
    FROM (
        SELECT 'val1%' AS val FROM dual
        UNION ALL
        SELECT 'val2%' AS val FROM dual
        -- ...
        -- or simply use an subquery here
    WHERE t.my_col LIKE val

How to make a radio button look like a toggle button

Here's my version of that nice CSS solution JS Fiddle example posted above.


<div id="donate">
    <label class="blue"><input type="radio" name="toggle"><span>$20</span></label>
    <label class="green"><input type="radio" name="toggle"><span>$50</span></label>
    <label class="yellow"><input type="radio" name="toggle"><span>$100</span></label>
    <label class="pink"><input type="radio" name="toggle"><span>$500</span></label>
    <label class="purple"><input type="radio" name="toggle"><span>$1000</span></label>


body {

#donate {


#donate label {
    border:1px solid #D0D0D0;


#donate label span {
    font-size: 32px;
    padding:13px 0px;

#donate label input {

#donate input:checked + span {

#donate .yellow {

#donate .blue {

#donate .pink {

#donate .green {
#donate .purple {

Styled with coloured buttons :)

Method Call Chaining; returning a pointer vs a reference?

The difference between pointers and references is quite simple: a pointer can be null, a reference can not.

Examine your API, if it makes sense for null to be able to be returned, possibly to indicate an error, use a pointer, otherwise use a reference. If you do use a pointer, you should add checks to see if it's null (and such checks may slow down your code).

Here it looks like references are more appropriate.

How do I make Git use the editor of my choice for commits?

Just because I came here looking for a one-time solution (in my case, I usually use vim but this one time I wanted to use VS Code) for a single command and others might want to know as well:

GIT_EDITOR='code -w' git rebase -i …

Here's my git/hub version just for context:

git version 2.24.2 (Apple Git-127)
hub version 2.14.1

Convert ASCII TO UTF-8 Encoding

Use utf8_encode()

Man page can be found here

Also read this article from Joel on Software. It provides an excellent explanation if what Unicode is and how it works.

Replace console output in Python

If I understood well (not sure) you want to print using <CR> and not <LR>?

If so this is possible, as long the console terminal allows this (it will break when output si redirected to a file).

from __future__ import print_function
print("count x\r", file=sys.stdout, end=" ")

Opening XML page shows "This XML file does not appear to have any style information associated with it."

This XML file does not appear to have any style information associated with it. The document tree is shown below.

You will get this error in the client side when the client (the webbrowser) for some reason interprets the HTTP response content as text/xml instead of text/html and the parsed XML tree doesn't have any XML-stylesheet. In other words, the webbrowser incorrectly parsed the retrieved HTTP response content as XML instead of as HTML due to the wrong or missing HTTP response content type.

In case of JSF/Facelets files which have the default extension of .xhtml, that can in turn happen if the HTTP request hasn't invoked the FacesServlet and thus it wasn't able to parse the Facelets file and generate the desired HTML output based on the XHTML source code. Firefox is then merely guessing the HTTP response content type based on the .xhtml file extension which is in your Firefox configuration apparently by default interpreted as text/xml.

You need to make sure that the HTTP request URL, as you see in browser's address bar, matches the <url-pattern> of the FacesServlet as registered in webapp's web.xml, so that it will be invoked and be able to generate the desired HTML output based on the XHTML source code. If it's for example *.jsf, then you need to open the page by /some.jsf instead of /some.xhtml. Alternatively, you can also just change the <url-pattern> to *.xhtml. This way you never need to fiddle with virtual URLs.

See also:

Note thus that you don't actually need a XML stylesheet. This all was just misinterpretation by the webbrowser while trying to do its best to make something presentable out of the retrieved HTTP response content. It should actually have retrieved the properly generated HTML output, Firefox surely knows precisely how to deal with HTML content.

How can I play sound in Java?

I didn't want to have so many lines of code just to play a simple damn sound. This can work if you have the JavaFX package (already included in my jdk 8).

private static void playSound(String sound){
    // cl is the ClassLoader for the current class, ie. CurrentClass.class.getClassLoader();
    URL file = cl.getResource(sound);
    final Media media = new Media(file.toString());
    final MediaPlayer mediaPlayer = new MediaPlayer(media);;

Notice : You need to initialize JavaFX. A quick way to do that, is to call the constructor of JFXPanel() once in your app :

    JFXPanel fxPanel = new JFXPanel();

Class Not Found: Empty Test Suite in IntelliJ

solved by manually run testClasses task before running unit test.

How to make a div center align in HTML

it depends if your div is in position: absolute / fixed or relative / static

for position: absolute & fixed

<div style="position: absolute; /*or fixed*/;
width: 50%;
height: 300px;
left: 50%;
margin: 0 0 0 -25%">blblablbalba</div>

The trick here is to have a negative margin half the width of the object

for position: relative & static

<div style="position: relative; /*or static*/;
width: 50%;
height: 300px;
margin: 0 auto">blblablbalba</div>

for both techniques, it is imperative to set the width.

How to change value of a request parameter in laravel

Use add

$request->request->add(['img' => $img]);

Best timestamp format for CSV/Excel?

So, weirdly excel imports a csv date in different ways. And, displays them differently depending on the format used in the csv file. Unfortunately the ISO 8061 format comes in as a string. Which prevents you from possibly reformatting the date yourself.

All the ones the do come in as a date... contain the entire information... but they format differently... if you don't like it you can choose a new format for the column in excel and it will work. (Note: you can tell it came in as a valid date/time as it will right justify... if it comes in as a string it will left justify)

Here are formats I tested:

"yyyy-MM-dd" shows up as a date of course when opened in excel. (also "MM/dd/yyyy" works)

"yyyy-MM-dd HH:mm:ss" default display format is "MM/dd/yyyy HH:mm" (date and time w/out seconds)

"yyyy-MM-dd HH:mm:ss.fff" default display format is "HH:mm:ss" (time only w/ seconds)

What is wrong with my SQL here? #1089 - Incorrect prefix key

Problem is the same for me in phpMyAdmin. I just created a table without any const. Later I modified the ID to a Primary key. Then I changed the ID to Auto-inc. That solved the issue.


[Ljava.lang.Object; cannot be cast to

I've faced such an issue and dig tones of material. So, to avoid ugly iteration you can simply tune your hql:

You need to frame your query like this

select entity from Entity as entity where ...

Also check such case, it perfectly works for me:

public List<User> findByRole(String role) {

    Query query = sessionFactory.getCurrentSession().createQuery("select user from User user join user.userRoles where role_name=:role_name");
    query.setString("role_name", role);
    List<User> users = (List<User>) query.list();
    return users;

So here we are extracting object from query, not a bunch of fields. Also it's looks much more pretty.

What is the difference between call and apply?

It is useful at times for one object to borrow the function of another object, meaning that the borrowing object simply executes the lent function as if it were its own.

A small code example:

var friend = {
    car: false,
    lendCar: function ( canLend ){ = canLend;


var me = {
    car: false,
    gotCar: function(){
      return === true;

console.log(me.gotCar()); // false, true); 

console.log(me.gotCar()); // true

friend.lendCar.apply(me, [false]);

console.log(me.gotCar()); // false

These methods are very useful for giving objects temporary functionality.

What is the purpose of the single underscore "_" variable in Python?

_ has 3 main conventional uses in Python:

  1. To hold the result of the last executed expression(/statement) in an interactive interpreter session (see docs). This precedent was set by the standard CPython interpreter, and other interpreters have followed suit

  2. For translation lookup in i18n (see the gettext documentation for example), as in code like

    raise forms.ValidationError(_("Please enter a correct username"))
  3. As a general purpose "throwaway" variable name:

    1. To indicate that part of a function result is being deliberately ignored (Conceptually, it is being discarded.), as in code like:

      label, has_label, _ = text.partition(':')
    2. As part of a function definition (using either def or lambda), where the signature is fixed (e.g. by a callback or parent class API), but this particular function implementation doesn't need all of the parameters, as in code like:

      def callback(_):
          return True

      [For a long time this answer didn't list this use case, but it came up often enough, as noted here, to be worth listing explicitly.]

    This use case can conflict with the translation lookup use case, so it is necessary to avoid using _ as a throwaway variable in any code block that also uses it for i18n translation (many folks prefer a double-underscore, __, as their throwaway variable for exactly this reason).

    Linters often recognize this use case. For example year, month, day = date() will raise a lint warning if day is not used later in the code. The fix, if day is truly not needed, is to write year, month, _ = date(). Same with lambda functions, lambda arg: 1.0 creates a function requiring one argument but not using it, which will be caught by lint. The fix is to write lambda _: 1.0. An unused variable is often hiding a bug/typo (e.g. set day but use dya in the next line).

How to create XML file with specific structure in Java

You can use the JDOM library in Java. Define your tags as Element objects, document your elements with Document Class, and build your xml file with SAXBuilder. Try this example:

//Root Element
Element root=new Element("CONFIGURATION");
Document doc=new Document();
//Element 1
Element child1=new Element("BROWSER");
//Element 1 Content
//Element 2
Element child2=new Element("BASE");
//Element 2 Content
//Element 3
Element child3=new Element("EMPLOYEE");
//Element 3 --> In this case this element has another element with Content
child3.addContent(new Element("EMP_NAME").addContent("Anhorn, Irene"));

//Add it in the root Element
//Define root element like root
//Create the XML
XMLOutputter outter=new XMLOutputter();
outter.output(doc, new FileWriter(new File("myxml.xml")));

How to dynamically add and remove form fields in Angular 2

addAccordian(type, data) { console.log(type, data);

let form = this.form;

if (!form.controls[type]) {
  let ownerAccordian = new FormArray([]);
  const group = new FormGroup({});
    this.applicationService.createControlWithGroup(data, group)
  form.controls[type] = ownerAccordian;
} else {
  const group = new FormGroup({});
    this.applicationService.createControlWithGroup(data, group)


Oracle SQL Developer: Unable to find a JVM

Version 1.5 is very, very old.

In the latest builds, we support 32 and 64 bit JDKs. In version 4.0, we find the JDK for you on Windows. If the software can't find it, it prompts for that path.

That path would look something like this C:\Java\jdk1.7.0_45

You can read more about this here.

What is the best way to delete a component with CLI

Answer for Angular 2+

Remove component from imports and declaration array of app.modules.ts.

Second check its reference is added in other module, if yes then remove it and

finally delete that component Manually from app and you are done.

Or you can do it in reverse order also.

phpMyAdmin access denied for user 'root'@'localhost' (using password: NO)

This is the Different Solution, Check if your Services are running correctly, if WAMP icon showing orange color, and 2 out of 3 services are running it's showing, then this solution will work . Root cause:

If in your system mysql was there, later you installed WAMP then again one MYSQL will install as WAMP package, default port for MYSQL is 3306 , So in both mysql the port will be 3306, which is a port conflict, So just change the port it will work fine. Steps to change the Port.

  1. Right click the WAMP icon.
  2. Chose Tool
  3. Change the port in Port used by MySql Section

Creating an Array from a Range in VBA

Just define the variable as a variant, and make them equal:

Dim DirArray As Variant
DirArray = Range("a1:a5").Value

No need for the Array command.

MySql sum elements of a column

  sum(a) as atotal,
  sum(b) as btotal,
  sum(c) as ctotal
  yourtable t
where in (1, 2, 3)

estimating of testing effort as a percentage of development time

Are you talking about automated unit/integration tests or manual tests?

For the former, my rule of thumb (based on measurements) is 40-50% added to development time i.e. if developing a use case takes 10 days (before an QA and serious bugfixing happens), writing good tests takes another 4 to 5 days - though this should best happen before and during development, not afterwards.

How to resolve "Error: bad index – Fatal: index file corrupt" when using Git

None of the existing answers worked for me.

I was using worktrees, so there is no .git folder.

You'll need to go back to your main repo. Inside that, delete .git/worktrees/<name_of_tree>/index

Then run git reset as per other answers.

How to pass parameters in GET requests with jQuery

The data parameter of ajax method allows you send data to server side.On server side you can request the data.See the code

var id=5;
    type: "get",
    url: "url of server side script",
    success: function(res){

At server side receive it using $_GET variable.


Hide axis values but keep axis tick labels in matplotlib

Not sure this is the best way, but you can certainly replace the tick labels like this:

import matplotlib.pyplot as plt
x = range(10)
y = range(10)
plt.xticks(x," ")

In Python 3.4 this generates a simple line plot with no tick labels on the x-axis. A simple example is here:

This related question also has some better suggestions: Hiding axis text in matplotlib plots

I'm new to python. Your mileage may vary in earlier versions. Maybe others can help?

How to convert an OrderedDict into a regular dict in python3

>>> from collections import OrderedDict
>>> OrderedDict([('method', 'constant'), ('data', '1.225')])
OrderedDict([('method', 'constant'), ('data', '1.225')])
>>> dict(OrderedDict([('method', 'constant'), ('data', '1.225')]))
{'data': '1.225', 'method': 'constant'}

However, to store it in a database it'd be much better to convert it to a format such as JSON or Pickle. With Pickle you even preserve the order!

Escape a string in SQL Server so that it is safe to use in LIKE expression

To escape special characters in a LIKE expression you prefix them with an escape character. You get to choose which escape char to use with the ESCAPE keyword. (MSDN Ref)

For example this escapes the % symbol, using \ as the escape char:

select * from table where myfield like '%15\% off%' ESCAPE '\'

If you don't know what characters will be in your string, and you don't want to treat them as wildcards, you can prefix all wildcard characters with an escape char, eg:

set @myString = replace( 
                replace( @myString
                ,    '\', '\\' )
                ,    '%', '\%' )
                ,    '_', '\_' )
                ,    '[', '\[' )

(Note that you have to escape your escape char too, and make sure that's the inner replace so you don't escape the ones added from the other replace statements). Then you can use something like this:

select * from table where myfield like '%' + @myString + '%' ESCAPE '\'

Also remember to allocate more space for your @myString variable as it will become longer with the string replacement.

Change working directory in my current shell context when running Node script

What you are trying to do is not possible. The reason for this is that in a POSIX system (Linux, OSX, etc), a child process cannot modify the environment of a parent process. This includes modifying the parent process's working directory and environment variables.

When you are on the commandline and you go to execute your Node script, your current process (bash, zsh, whatever) spawns a new process which has it's own environment, typically a copy of your current environment (it is possible to change this via system calls; but that's beyond the scope of this reply), allowing that process to do whatever it needs to do in complete isolation. When the subprocess exits, control is handed back to your shell's process, where the environment hasn't been affected.

There are a lot of reasons for this, but for one, imagine that you executed a script in the background (via ./foo.js &) and as it ran, it started changing your working directory or overriding your PATH. That would be a nightmare.

If you need to perform some actions that require changing your working directory of your shell, you'll need to write a function in your shell. For example, if you're running Bash, you could put this in your ~/.bash_profile:

do_cool_thing() {
  cd "/Users"
  echo "Hey, I'm in $PWD"

and then this cool thing is doable:

$ pwd
$ do_cool_thing
Hey, I'm in /Users
$ pwd

If you need to do more complex things in addition, you could always call out to your nodejs script from that function.

This is the only way you can accomplish what you're trying to do.

How do I get LaTeX to hyphenate a word that contains a dash?

The problem (as KennyTM noted) is that LaTeX won't hyphenate words with dashes in them. Luckily, there's a standard package (part of ncctools) that addresses that very problem, called extdash. This defines new hyphen and dash commands that do not disrupt hyphenation, and which can allow or prevent line breaks at the hyphen/dash. I prefer to use it with the shortcuts option, so I can use, e.g., \-/ rather than \Hyphdash. Here's what you want:

\usepackage[shortcuts]{extdash} ... multi\-/disciplinary

To prevent breaking at that hyphen, use multi\=/disciplinary

(Aside: The Chicago Manual of Style advises dropping the hyphens attaching affixes like 'multi', unless the word is ambiguous or unintelligible without it.)

How to change the port number for Asp.Net core app?

3 files have to changed appsettings.json (see the last section - kestrel ), launchsettings.json - applicationurl commented out, and a 2 lines change in Startup.cs

Add below code in appsettings.json file and port to any as you wish.


 "Kestrel": {

   "Endpoints": {

     "Http": {

       "Url": "http://localhost:5003"





Modify Startup.cs with below lines.

using Microsoft.AspNetCore.Server.Kestrel.Core;


uppercase first character in a variable with bash

What if the first character is not a letter (but a tab, a space, and a escaped double quote)? We'd better test it until we find a letter! So:

S='  \"ó foo bar\"'
until [[ ${S:$N:1} =~ [[:alpha:]] ]]; do N=$[$N+1]; done
#F=`echo ${S:$N:1} | tr [:lower:] [:upper:]`
#F=`echo ${S:$N:1} | sed -E -e 's/./\u&/'` #other option
F=`echo ${S:$N:1}
F=`echo ${F} #pure Bash solution to "upper"
echo "$F"${S:(($N+1))} #without garbage
echo '='${S:0:(($N))}"$F"${S:(($N+1))}'=' #garbage preserved

Foo bar
= \"Foo bar=

How to sort an object array by date property?

I recommend GitHub: Array sortBy - a best implementation of sortBy method which uses the Schwartzian transform

But for now we are going to try this approach Gist: sortBy-old.js.
Let's create a method to sort arrays being able to arrange objects by some property.

Creating the sorting function

var sortBy = (function () {
  var toString = Object.prototype.toString,
      // default parser function
      parse = function (x) { return x; },
      // gets the item to be sorted
      getItem = function (x) {
        var isObject = x != null && typeof x === "object";
        var isProp = isObject && this.prop in x;
        return this.parser(isProp ? x[this.prop] : x);
   * Sorts an array of elements.
   * @param {Array} array: the collection to sort
   * @param {Object} cfg: the configuration options
   * @property {String}   cfg.prop: property name (if it is an Array of objects)
   * @property {Boolean}  cfg.desc: determines whether the sort is descending
   * @property {Function} cfg.parser: function to parse the items to expected type
   * @return {Array}
  return function sortby (array, cfg) {
    if (!(array instanceof Array && array.length)) return [];
    if ( !== "[object Object]") cfg = {};
    if (typeof cfg.parser !== "function") cfg.parser = parse;
    cfg.desc = !!cfg.desc ? -1 : 1;
    return array.sort(function (a, b) {
      a =, a);
      b =, b);
      return cfg.desc * (a < b ? -1 : +(a > b));

Setting unsorted data

var data = [
  {date: "2011-11-14T17:25:45Z", quantity: 2, total: 200, tip: 0,   type: "cash"},
  {date: "2011-11-14T16:28:54Z", quantity: 1, total: 300, tip: 200, type: "visa"},
  {date: "2011-11-14T16:30:43Z", quantity: 2, total: 90,  tip: 0,   type: "tab"},
  {date: "2011-11-14T17:22:59Z", quantity: 2, total: 90,  tip: 0,   type: "tab"},
  {date: "2011-11-14T16:53:41Z", quantity: 2, total: 90,  tip: 0,   type: "tab"},
  {date: "2011-11-14T16:48:46Z", quantity: 2, total: 90,  tip: 0,   type: "tab"},
  {date: "2011-11-31T17:29:52Z", quantity: 1, total: 200, tip: 100, type: "visa"},
  {date: "2011-11-01T16:17:54Z", quantity: 2, total: 190, tip: 100, type: "tab"},
  {date: "2011-11-14T16:58:03Z", quantity: 2, total: 90,  tip: 0,   type: "tab"},
  {date: "2011-11-14T16:20:19Z", quantity: 2, total: 190, tip: 100, type: "tab"},
  {date: "2011-11-14T17:07:21Z", quantity: 2, total: 90,  tip: 0,   type: "tab"},
  {date: "2011-11-14T16:54:06Z", quantity: 1, total: 100, tip: 0,   type: "cash"}

Using it

Finally, we arrange the array, by "date" property as string

//sort the object by a property (ascending)
//sorting takes into account uppercase and lowercase
sortBy(data, { prop: "date" });

If you want to ignore letter case, set the "parser" callback:

//sort the object by a property (descending)
//sorting ignores uppercase and lowercase
sortBy(data, {
    prop: "date",
    desc: true,
    parser: function (item) {
        //ignore case sensitive
        return item.toUpperCase();

If you want to treat the "date" field as Date type:

//sort the object by a property (ascending)
//sorting parses each item to Date type
sortBy(data, {
    prop: "date",
    parser: function (item) {
        return new Date(item);

Here you can play with the above example:

Casting string to enum

As an extra, you can take the Enum.Parse answers already provided and put them in an easy-to-use static method in a helper class.

public static T ParseEnum<T>(string value)
    return (T)Enum.Parse(typeof(T), value, ignoreCase: true);

And use it like so:

   Content = ParseEnum<ContentEnum>(fileContentMessage);

Especially helpful if you have lots of (different) Enums to parse.

Calling a function within a Class method?

You can also use self::CONST instead of $this->CONST if you want to call a static variable or function of the current class.

Java 8 stream's .min() and .max(): why does this compile?

This works because Integer::min resolves to an implementation of the Comparator<Integer> interface.

The method reference of Integer::min resolves to Integer.min(int a, int b), resolved to IntBinaryOperator, and presumably autoboxing occurs somewhere making it a BinaryOperator<Integer>.

And the min() resp max() methods of the Stream<Integer> ask the Comparator<Integer> interface to be implemented.
Now this resolves to the single method Integer compareTo(Integer o1, Integer o2). Which is of type BinaryOperator<Integer>.

And thus the magic has happened as both methods are a BinaryOperator<Integer>.

QtCreator: No valid kits found

Though OP is asking about Windows, this error also occurs on Ubuntu Linux and Google lists this result first when you search for the error"QtCreator: No valid kits found".

On Ubuntu this is solved by running:

For Qt5:

sudo apt-get install qt5-default

For Qt4:

sudo apt-get install qt4-dev-tools libqt4-dev libqt4-core libqt4-gui

This question is answered here and here, though those entries are less SEO-friendly...

How to hide columns in an ASP.NET GridView with auto-generated columns?

Similar to accepted answer but allows use of ColumnNames and binds to RowDataBound().

Dictionary<string, int> _headerIndiciesForAbcGridView = null;

protected void abcGridView_RowDataBound(object sender, GridViewRowEventArgs e)
    if (_headerIndiciesForAbcGridView == null) // builds once per http request
        int index = 0;
        _headerIndiciesForAbcGridView = ((Table)((GridView)sender).Controls[0]).Rows[0].Cells
            .ToDictionary(c => c.Text, c => index++);

    e.Row.Cells[_headerIndiciesForAbcGridView["theColumnName"]].Visible = false;

Not sure if it works with RowCreated().

How to specify in crontab by what user to run script?

Instead of creating a crontab to run as the root user, create a crontab for the user that you want to run the script. In your case, crontab -u www-data -e will edit the crontab for the www-data user. Just put your full command in there and remove it from the root user's crontab.

Cut off text in string after/before separator in powershell

$name -replace ";*",""

You were close, but you used the syntax of a wildcard expresson rather than a regular expression, which is what the -replace operator expects.

Therefore (hash sequence shortened):

PS> 'test.txt ; 131 136 80 89 119 17 60 123 210 121 188' -replace '\s*;.*'


  • Omitting the substitution-text operand (the 2nd RHS operand) implicitly uses "" (the empty string), i.e. it effectively removes what the regex matched.

  • .* is what represents a potentially empty run (*) of characters (.) in a regex - it is the regex equivalent of * by itself in a wildcard expression.

  • Adding \s* before the ; in the regex also removes trailing whitespace (\s) after the filename.

  • I've used '...' rather than "..." to enclose the regex, so as to prevent confusion between what PowerShell expands up front (see expandable strings in PowerShell and what the .NET regex engine sees.

How to return a class object by reference in C++?

You're probably returning an object that's on the stack. That is, return_Object() probably looks like this:

Object& return_Object()
    Object object_to_return;
    // ... do stuff ...

    return object_to_return;

If this is what you're doing, you're out of luck - object_to_return has gone out of scope and been destructed at the end of return_Object, so myObject refers to a non-existent object. You either need to return by value, or return an Object declared in a wider scope or newed onto the heap.

Invalid postback or callback argument. Event validation is enabled using '<pages enableEventValidation="true"/>'

you try something like that,in your .aspx page



you feel free to ask any question!

What are SP (stack) and LR in ARM?

LR is link register used to hold the return address for a function call.

SP is stack pointer. The stack is generally used to hold "automatic" variables and context/parameters across function calls. Conceptually you can think of the "stack" as a place where you "pile" your data. You keep "stacking" one piece of data over the other and the stack pointer tells you how "high" your "stack" of data is. You can remove data from the "top" of the "stack" and make it shorter.

From the ARM architecture reference:

SP, the Stack Pointer

Register R13 is used as a pointer to the active stack.

In Thumb code, most instructions cannot access SP. The only instructions that can access SP are those designed to use SP as a stack pointer. The use of SP for any purpose other than as a stack pointer is deprecated. Note Using SP for any purpose other than as a stack pointer is likely to break the requirements of operating systems, debuggers, and other software systems, causing them to malfunction.

LR, the Link Register

Register R14 is used to store the return address from a subroutine. At other times, LR can be used for other purposes.

When a BL or BLX instruction performs a subroutine call, LR is set to the subroutine return address. To perform a subroutine return, copy LR back to the program counter. This is typically done in one of two ways, after entering the subroutine with a BL or BLX instruction:

• Return with a BX LR instruction.

• On subroutine entry, store LR to the stack with an instruction of the form: PUSH {,LR} and use a matching instruction to return: POP {,PC} ...

This link gives an example of a trivial subroutine.

Here is an example of how registers are saved on the stack prior to a call and then popped back to restore their content.

no suitable HttpMessageConverter found for response type

If you are using Spring Boot, you might want to make sure you have the Jackson dependency in your classpath. You can do this manually via:


Or you can use the web starter:


How to execute shell command in Javascript

Another post on this topic with a nice jQuery/Ajax/PHP solution:

shell scripting and jQuery

Can a CSV file have a comment?

The CSV "standard" (such as it is) does not dictate how comments should be handled, no, it's up to the application to establish a convention and stick with it.

How to provide shadow to Button

For android version 5.0 & above

try the Elevation for other views..


For Buttons,


button_state_list_animator.xml -

below 5.0 version,

For all views,


My output:

enter image description here

Convert Promise to Observable

You can also use a Subject and trigger its next() function from promise. See sample below:

Add code like below ( I used service )

class UserService {_x000D_
  private createUserSubject: Subject < any > ;_x000D_
  createUserWithEmailAndPassword() {_x000D_
    if (this.createUserSubject) {_x000D_
      return this.createUserSubject;_x000D_
    } else {_x000D_
      this.createUserSubject = new Subject < any > ();_x000D_
        .then(function(firebaseUser) {_x000D_
          // do something to update your UI component_x000D_
          // pass user object to UI component_x000D_
        .catch(function(error) {_x000D_
          // Handle Errors here._x000D_
          var errorCode = error.code;_x000D_
          var errorMessage = error.message;_x000D_
          // ..._x000D_

Create User From Component like below

class UserComponent {_x000D_
  constructor(private userService: UserService) {_x000D_
    this.userService.createUserWithEmailAndPassword().subscribe(user => console.log(user), error => console.log(error);_x000D_

Auto-size dynamic text to fill fixed size container

I didn't find any of the previous solutions to be adequate enough due to bad performance, so I made my own that uses simple math instead of looping. Should work fine in all browsers as well.

According to this performance test case it is much faster then the other solutions found here.

(function($) {
    $.fn.textfill = function(maxFontSize) {
        maxFontSize = parseInt(maxFontSize, 10);
        return this.each(function(){
            var ourText = $("span", this),
                parent = ourText.parent(),
                maxHeight = parent.height(),
                maxWidth = parent.width(),
                fontSize = parseInt(ourText.css("fontSize"), 10),
                multiplier = maxWidth/ourText.width(),
                newSize = (fontSize*(multiplier-0.1));
                (maxFontSize > 0 && newSize > maxFontSize) ? 
                    maxFontSize : 

If you want to contribute I've added this to Gist.

What is the "assert" function?

C++11 N3337 standard draft

19.3 Assertions

1 The header <cassert>, described in (Table 42), provides a macro for documenting C ++ program assertions and a mechanism for disabling the assertion checks.

2 The contents are the same as the Standard C library header <assert.h>.

C99 N1256 standard draft

7.2 Diagnostics <assert.h>

1 The header <assert.h> defines the assert macro and refers to another macro, NDEBUG which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the point in the source file where <assert.h> is included, the assert macro is defined simply as

 #define assert(ignore) ((void)0)

The assert macro is redefined according to the current state of NDEBUG each time that <assert.h> is included.

2. The assert macro shall be implemented as a macro, not as an actual function. If the macro definition is suppressed in order to access an actual function, the behavior is undefined.

7.2.1 Program diagnostics The assert macro



#include <assert.h>
void assert(scalar expression);


2 The assert macro puts diagnostic tests into programs; it expands to a void expression. When it is executed, if expression (which shall have a scalar type) is false (that is, compares equal to 0), the assert macro writes information about the particular call that failed (including the text of the argument, the name of the source file, the source line number, and the name of the enclosing function — the latter are respectively the values of the preprocessing macros __FILE__ and __LINE__ and of the identifier __func__) on the standard error stream in an implementation-defined format. 165) It then calls the abort function.


3 The assert macro returns no value.

Windows batch script to unhide files hidden by virus

echo "Enter Drive letter" 
set /p driveletter=

attrib -s -h -a /s /d  %driveletter%:\*.*

Git says remote ref does not exist when I delete remote branch

git push origin --delete origin/test 

should work as well

How to decode a QR-code image in (preferably pure) Python?

For Windows using ZBar


To decode:

from PIL import Image
from pyzbar import pyzbar

img ='My-Image.jpg')
output = pyzbar.decode(img)

Alternatively, you can also try using ZBarLight by setting it up as mentioned here:

How to pass List<String> in post method using Spring MVC?

I had the same use case, You can change your method defination in the following way :

@RequestMapping(value = "/saveFruits", method = RequestMethod.POST, 
    consumes = "application/json")
public ResultObject saveFruits(@RequestBody Map<String,List<String>> fruits) {

The only problem is it accepts any key in place of "fruits" but You can easily get rid of a wrapper if it is not big functionality.

Laravel Eloquent compare date from datetime field

Have you considered using:

where('date', '<', '2014-08-11')

You should avoid using the DATE() function on indexed columns in MySQL, as this prevents the engine from using the index.


As there seems to be some disagreement about the importance of DATE() and indexes, I have created a fiddle that demonstrates the difference, see POSSIBLE KEYS.

Internet Explorer cache location

In windows serven and 8 and later in this location can find IE Cache


Update int column in table with unique incrementing values

Assuming that you have a primary key for this table (you should have), as well as using a CTE or a WITH, it is also possible to use an update with a self-join to the same table:

SET a.interfaceId = b.sequence
FROM prices a
   SELECT ROW_NUMBER() OVER ( ORDER BY b.priceId ) + ( SELECT MAX( interfaceId ) + 1 FROM prices ) AS sequence, b.priceId
   FROM prices b
   WHERE b.interfaceId IS NULL
) b ON b.priceId = a.priceId

I have assumed that the primary key is price-id.

The derived table, alias b, is used to generated the sequence via the ROW_NUMBER() function together with the primary key column(s). For each row where the column interface-id is NULL, this will generate a row with a unique sequence value together with the primary key value.

It is possible to order the sequence in some other order rather than the primary key.

The sequence is offset by the current MAX interface-id + 1 via a sub-query. The MAX() function ignores NULL values.

The WHERE clause limits the update to those rows that are NULL.

The derived table is then joined to the same table, alias a, joining on the primary key column(s) with the column to be updated set to the generated sequence.

How to send a JSON object using html form data

I'm late but I need to say for those who need an object, using only html, there's a way. In some server side frameworks like PHP you can write the follow code:

<form action="myurl" method="POST" name="myForm">
        <p><label for="first_name">First Name:</label>
        <input type="text" name="name[first]" id="fname"></p>

        <p><label for="last_name">Last Name:</label>
        <input type="text" name="name[last]" id="lname"></p>

        <input value="Submit" type="submit">

So, we need setup the name of the input as object[property] for got an object. In the above example, we got a data with the follow JSON:

"name": {
  "first": "some data",
  "last": "some data"

Media Queries - In between two widths

@Jonathan Sampson i think your solution is wrong if you use multiple @media.

You should use (min-width first):

@media screen and (min-width:400px) and (max-width:900px){

Headers and client library minor version mismatch

My hosting company told me to fix this by deactivating "mysqli" and activating "nd_mysqli" in the php extensions.

The error is gone, but I don't have the knowledge to understand if this is the right method to fix this.

"The following SDK components were not installed: sys-img-x86-addon-google_apis-google-22 and addon-google_apis-google-22"

When you are installing Android Studio, under Install type do not use standard setting, use custom setting instead, and check all the option boxes in the next step.

Class method differences in Python: bound, unbound and static

When you call a class member, Python automatically uses a reference to the object as the first parameter. The variable self actually means nothing, it's just a coding convention. You could call it gargaloo if you wanted. That said, the call to method_two would raise a TypeError, because Python is automatically trying to pass a parameter (the reference to its parent object) to a method that was defined as having no parameters.

To actually make it work, you could append this to your class definition:

method_two = staticmethod(method_two)

or you could use the @staticmethod function decorator.

Where's my invalid character (ORA-00911)

Of the top of my head, can you try to use the 'q' operator for the string literal

something like

insert all
  into domo_queries values (q'[select 
substr(to_char(max_data),1,4) as year,
substr(to_char(max_data),5,6) as month,
from dss_fin_user.acq_dashboard_src_load_success
where source = 'CHQ PeopleSoft FS']')
select * from dual;

Note that the single quotes of your predicate are not escaped, and the string sits between q'[...]'.

How can I disable ReSharper in Visual Studio and enable it again?

If resharper is completely missing from the options menu, it could be because the extension itself has been disabled.

In Visual Studio 2017 ReSharper 2018.X.X can be enabled and disabled by going to Help > Manage Visual Studio Performance. Then select JetBrains ReSharper ... under Extensions.

enter image description here

In Visual Studio 2019, you would go under Extensions->Manage Extensions->Installed

VHDL - How should I create a clock in a testbench?

If multiple clock are generated with different frequencies, then clock generation can be simplified if a procedure is called as concurrent procedure call. The time resolution issue, mentioned by Martin Thompson, may be mitigated a little by using different high and low time in the procedure. The test bench with procedure for clock generation is:

library ieee;
use ieee.std_logic_1164.all;

entity tb is
end entity;

architecture sim of tb is

  -- Procedure for clock generation
  procedure clk_gen(signal clk : out std_logic; constant FREQ : real) is
    constant PERIOD    : time := 1 sec / FREQ;        -- Full period
    constant HIGH_TIME : time := PERIOD / 2;          -- High time
    constant LOW_TIME  : time := PERIOD - HIGH_TIME;  -- Low time; always >= HIGH_TIME
    -- Check the arguments
    assert (HIGH_TIME /= 0 fs) report "clk_plain: High time is zero; time resolution to large for frequency" severity FAILURE;
    -- Generate a clock cycle
      clk <= '1';
      wait for HIGH_TIME;
      clk <= '0';
      wait for LOW_TIME;
    end loop;
  end procedure;

  -- Clock frequency and signal
  signal clk_166 : std_logic;
  signal clk_125 : std_logic;


  -- Clock generation with concurrent procedure call
  clk_gen(clk_166, 166.667E6);  -- 166.667 MHz clock
  clk_gen(clk_125, 125.000E6);  -- 125.000 MHz clock

  -- Time resolution show
  assert FALSE report "Time resolution: " & time'image(time'succ(0 fs)) severity NOTE;

end architecture;

The time resolution is printed on the terminal for information, using the concurrent assert last in the test bench.

If the clk_gen procedure is placed in a separate package, then reuse from test bench to test bench becomes straight forward.

Waveform for clocks are shown in figure below.

Waveforms for clk_166 and clk_125

An more advanced clock generator can also be created in the procedure, which can adjust the period over time to match the requested frequency despite the limitation by time resolution. This is shown here:

-- Advanced procedure for clock generation, with period adjust to match frequency over time, and run control by signal
procedure clk_gen(signal clk : out std_logic; constant FREQ : real; PHASE : time := 0 fs; signal run : std_logic) is
  constant HIGH_TIME   : time := 0.5 sec / FREQ;  -- High time as fixed value
  variable low_time_v  : time;                    -- Low time calculated per cycle; always >= HIGH_TIME
  variable cycles_v    : real := 0.0;             -- Number of cycles
  variable freq_time_v : time := 0 fs;            -- Time used for generation of cycles
  -- Check the arguments
  assert (HIGH_TIME /= 0 fs) report "clk_gen: High time is zero; time resolution to large for frequency" severity FAILURE;
  -- Initial phase shift
  clk <= '0';
  wait for PHASE;
  -- Generate cycles
    -- Only high pulse if run is '1' or 'H'
    if (run = '1') or (run = 'H') then
      clk <= run;
    end if;
    wait for HIGH_TIME;
    -- Low part of cycle
    clk <= '0';
    low_time_v := 1 sec * ((cycles_v + 1.0) / FREQ) - freq_time_v - HIGH_TIME;  -- + 1.0 for cycle after current
    wait for low_time_v;
    -- Cycle counter and time passed update
    cycles_v := cycles_v + 1.0;
    freq_time_v := freq_time_v + HIGH_TIME + low_time_v;
  end loop;
end procedure;

Again reuse through a package will be nice.

Disable all table constraints in Oracle

SELECT 'ALTER TABLE '||substr(c.table_name,1,35)|| 
' DISABLE CONSTRAINT '||constraint_name||' ;' 
FROM user_constraints c, user_tables u 
WHERE c.table_name = u.table_name; 

This statement returns the commands which turn off all the constraints including primary key, foreign keys, and another constraints.

What's the function like sum() but for multiplication? product()?

There isn't one built in, but it's simple to roll your own, as demonstrated here:

import operator
def prod(factors):
    return reduce(operator.mul, factors, 1)

See answers to this question:

Which Python module is suitable for data manipulation in a list?

How to uninstall / completely remove Oracle 11g (client)?

Do everything suggested by ziesemer.

You may also want to :

  • Stop the Oracle-related services (before deleting them from the registry).
  • In the registry, look not only for entries named "Oracle" but also e.g. for "ODP".

jQuery click not working for dynamically created items

You have to add click event to an exist element. You can not add event to dom elements dynamic created. I you want to add event to them, you should bind event to an existed element using ".on".


.delegate should work,too.

How to set adaptive learning rate for GradientDescentOptimizer?

If you want to set specific learning rates for intervals of epochs like 0 < a < b < c < .... Then you can define your learning rate as a conditional tensor, conditional on the global step, and feed this as normal to the optimiser.

You could achieve this with a bunch of nested tf.cond statements, but its easier to build the tensor recursively:

def make_learning_rate_tensor(reduction_steps, learning_rates, global_step):
    assert len(reduction_steps) + 1 == len(learning_rates)
    if len(reduction_steps) == 1:
        return tf.cond(
            global_step < reduction_steps[0],
            lambda: learning_rates[0],
            lambda: learning_rates[1]
        return tf.cond(
            global_step < reduction_steps[0],
            lambda: learning_rates[0],
            lambda: make_learning_rate_tensor(

Then to use it you need to know how many training steps there are in a single epoch, so that we can use the global step to switch at the right time, and finally define the epochs and learning rates you want. So if I want the learning rates [0.1, 0.01, 0.001, 0.0001] during the epoch intervals of [0, 19], [20, 59], [60, 99], [100, \infty] respectively, I would do:

global_step = tf.train.get_or_create_global_step()
learning_rates = [0.1, 0.01, 0.001, 0.0001]
steps_per_epoch = 225
epochs_to_switch_at = [20, 60, 100]
epochs_to_switch_at = [x*steps_per_epoch for x in epochs_to_switch_at ]
learning_rate = make_learning_rate_tensor(epochs_to_switch_at , learning_rates, global_step)

How do I perform query filtering in django templates

I run into this problem on a regular basis and often use the "add a method" solution. However, there are definitely cases where "add a method" or "compute it in the view" don't work (or don't work well). E.g. when you are caching template fragments and need some non-trivial DB computation to produce it. You don't want to do the DB work unless you need to, but you won't know if you need to until you are deep in the template logic.

Some other possible solutions:

  1. Use the {% expr <expression> as <var_name> %} template tag found at The expression is any legal Python expression with your template's Context as your local scope.

  2. Change your template processor. Jinja2 ( has syntax that is almost identical to the Django template language, but with full Python power available. It's also faster. You can do this wholesale, or you might limit its use to templates that you are working on, but use Django's "safer" templates for designer-maintained pages.

How do I filter an array with AngularJS and use a property of the filtered object as the ng-model attribute?

Applying same filter in HTML with multiple columns, just example:

 variable = (array | filter : {Lookup1Id : subject.Lookup1Id, Lookup2Id : subject.Lookup2Id} : true)

Unable to find the requested .Net Framework Data Provider in Visual Studio 2010 Professional

its solved. Use nuget and search for the "ODP.NET, Managed Driver" invariant="Oracle.ManagedDataAccess.Client".

and install the package. it will resolve the issue for me.

How can I get my webapp's base URL in ASP.NET MVC?

Simply in one line get BaseUrl

string baseUrl = new Uri(Request.Url, Url.Content("~")).AbsoluteUri;

//output example:

vertical & horizontal lines in matplotlib

The pyplot functions you are calling, axhline() and axvline() draw lines that span a portion of the axis range, regardless of coordinates. The parameters xmin or ymin use value 0.0 as the minimum of the axis and 1.0 as the maximum of the axis.

Instead, use plt.plot((x1, x2), (y1, y2), 'k-') to draw a line from the point (x1, y1) to the point (x2, y2) in color k. See pyplot.plot.

Is there such a thing as min-font-size and max-font-size?

It works well with CSS.

I went through the same issues and fixed it as follow.

Use a fixed "px" size for maximum size at a specific width and above. Then for different smaller widths, use a relative "vw" as a percentage of the screen.

The result below is that it adjusts itself at screens below 960px but keep a fixed size above. Just a reminder, not to forget to add in the html doc in header:

<meta name="viewport" content="width=device-width">

Example in CSS:

@media all and (min-width: 960px) {
    font-size: 50px;

@media all and (max-width: 959px) and (min-width: 600px) {
    font-size: 5vw;

@media all and (max-width: 599px) and (min-width: 50px) {
    font-size: 6vw;

I hope it'll help!

Auto start node.js server on boot

Copied directly from this answer:

You could write a script in any language you want to automate this (even using nodejs) and then just install a shortcut to that script in the user's %appdata%\Microsoft\Windows\Start Menu\Programs\Startup folder

Bootstrap 3 .col-xs-offset-* doesn't work?

As of Boostrap 4.x, just as col-xs-6 is now just col-6

offset-xs-6 is now just offset-6.

Already tried it, definitely works.

Cannot create cache directory .. or directory is not writable. Proceeding without cache in Laravel

Change the group permission for the folder

sudo chown -R w3cert /home/w3cert/.composer/cache/repo/

and the Files folder too

sudo chown -R w3cert /home/w3cert/.composer/cache/files/

I'm assuming w3cert is your username, if not change the 4th parameter to your username.

If the problem still persists try

sudo chown -R w3cert /home/w3cert/.composer

Now, there is a chance that you won't be able to create your app directory, if that happens do the same for your html folder or the folder you are trying to create your laravel project in.

Hope this helps.

Plotting of 1-dimensional Gaussian distribution function

With the excellent matplotlib and numpy packages

from matplotlib import pyplot as mp
import numpy as np

def gaussian(x, mu, sig):
    return np.exp(-np.power(x - mu, 2.) / (2 * np.power(sig, 2.)))

x_values = np.linspace(-3, 3, 120)
for mu, sig in [(-1, 1), (0, 2), (2, 3)]:
    mp.plot(x_values, gaussian(x_values, mu, sig))

will produce something like plot showing one-dimensional gaussians produced by matplotlib

Composer: The requested PHP extension ext-intl * is missing from your system

For php.ini 5.6 version (check version using php -v)

;extension=php_intl.dll ; remove semicolon and keep like this extension=php_intl.dll

For php.ini 7.* version

;extension=intl ; remove semicolon and keep like this extension=intl

Note - After That Make Sure to Restart Your Xampp,Wamp Server in you Local Machine.

How can I download HTML source in C#


using System.Net;
using System.Net.Http;  // in LINQPad, also add a reference to System.Net.Http.dll

WebRequest req = HttpWebRequest.Create("");
req.Method = "GET";

string source;
using (StreamReader reader = new StreamReader(req.GetResponse().GetResponseStream()))
    source = reader.ReadToEnd();


Header div stays at top, vertical scrolling div below with scrollbar only attached to that div

Found the flex magic.

Here's an example of how to do a fixed header and a scrollable content. Code:

<!DOCTYPE html>
<html style="height: 100%">
    <meta charset=utf-8 />
    <title>Holy Grail</title>
    <!-- Reset browser defaults -->
    <link rel="stylesheet" href="reset.css">
  <body style="display: flex; height: 100%; flex-direction: column">
    <div style="flex: 1; overflow: auto">
        CONTENT - START<br/>
        for (var i=0 ; i<1000 ; ++i) {
          document.write(" Very long content!");
        <br/>CONTENT - END

* The advantage of the flex solution is that the content is independent of other parts of the layout. For example, the content doesn't need to know height of the header.

For a full Holy Grail implementation (header, footer, nav, side, and content), using flex display, go to here.

How to reset (clear) form through JavaScript?

Pure JS solution is as follows:

function clearForm(myFormElement) {

  var elements = myFormElement.elements;


  for(i=0; i<elements.length; i++) {

  field_type = elements[i].type.toLowerCase();

  switch(field_type) {

    case "text":
    case "password":
    case "textarea":
          case "hidden":

      elements[i].value = "";

    case "radio":
    case "checkbox":
        if (elements[i].checked) {
          elements[i].checked = false;

    case "select-one":
    case "select-multi":
                elements[i].selectedIndex = -1;


how to get yesterday's date in C#

string result = DateTime.Now.Date.AddDays(-1).ToString("yyyy-MM-dd");

Restart container within pod

kubectl exec -it POD_NAME -c CONTAINER_NAME bash - then kill 1

Assuming the container is run as root which is not recommended.

In my case when I changed the application config, I had to reboot the container which was used in a sidecar pattern, I would kill the PID for the spring boot application which is owned by the docker user.

how to align img inside the div to the right?

vertical-align:middle; text-align:right;

How to properly apply a lambda function into a pandas data frame column

You need mask:

sample['PR'] = sample['PR'].mask(sample['PR'] < 90, np.nan)

Another solution with loc and boolean indexing:

sample.loc[sample['PR'] < 90, 'PR'] = np.nan


import pandas as pd
import numpy as np

sample = pd.DataFrame({'PR':[10,100,40] })
print (sample)
0   10
1  100
2   40

sample['PR'] = sample['PR'].mask(sample['PR'] < 90, np.nan)
print (sample)
0    NaN
1  100.0
2    NaN
sample.loc[sample['PR'] < 90, 'PR'] = np.nan
print (sample)
0    NaN
1  100.0
2    NaN


Solution with apply:

sample['PR'] = sample['PR'].apply(lambda x: np.nan if x < 90 else x)

Timings len(df)=300k:

sample = pd.concat([sample]*100000).reset_index(drop=True)

In [853]: %timeit sample['PR'].apply(lambda x: np.nan if x < 90 else x)
10 loops, best of 3: 102 ms per loop

In [854]: %timeit sample['PR'].mask(sample['PR'] < 90, np.nan)
The slowest run took 4.28 times longer than the fastest. This could mean that an intermediate result is being cached.
100 loops, best of 3: 3.71 ms per loop

Responsive image map

responsive width && height

window.onload = function () {
        var ImageMap = function (map, img) {
                var n,
                    areas = map.getElementsByTagName('area'),
                    len = areas.length,
                    coords = [],
                    imgWidth = img.naturalWidth,
                    imgHeight = img.naturalHeight;
                for (n = 0; n < len; n++) {
                    coords[n] = areas[n].coords.split(',');
            this.resize = function () {
                var n, m, clen,
                    x = img.offsetWidth / imgWidth,
                    y = img.offsetHeight / imgHeight;
                    imgWidth = img.offsetWidth;
                    imgHeight = img.offsetHeight;
                for (n = 0; n < len; n++) {
                    clen = coords[n].length;
                    for (m = 0; m < clen; m +=2) {
                        coords[n][m] *= x;
                        coords[n][m+1] *= y;
                    areas[n].coords = coords[n].join(',');
                    return true;
                window.onresize = this.resize;
        imageMap = new ImageMap(document.getElementById('map_region'), document.getElementById('prepay_region'));

How do I download and save a file locally on iOS using objective C?

NSURLSession introduced in iOS 7, is the recommended SDK way of downloading a file. No need to import 3rd party libraries.

NSURL *url = [NSURL URLWithString:@""];
NSURLRequest *downloadRequest = [NSURLRequest requestWithURL:url];
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *urlSession = [NSURLSession sessionWithConfiguration:sessionConfig delegate:self delegateQueue:nil];
self.downloadTask = [self.urlSession downloadTaskWithRequest:downloadRequest];
[self.downloadTask resume];

You can then use the NSURLSessionDownloadDelegate delegate methods to monitor errors, download completion, download progress etc... There are inline block completion handler callback methods too if you prefer. Apples docs explain when you need to use one over the other.

Have a read of these articles: NSURLConnection to NSURLSession

URL Loading System Programming Guide

How do I declare and assign a variable on a single line in SQL

You've nearly got it:

DECLARE @myVariable nvarchar(max) = 'hello world';

See here for the docs

For the quotes, SQL Server uses apostrophes, not quotes:

DECLARE @myVariable nvarchar(max) = 'John said to Emily "Hey there Emily"';

Use double apostrophes if you need them in a string:

DECLARE @myVariable nvarchar(max) = 'John said to Emily ''Hey there Emily''';

How do I get this javascript to run every second?

You can use setTimeout to run the function/command once or setInterval to run the function/command at specified intervals.

var a = setTimeout("alert('run just one time')",500);
var b = setInterval("alert('run each 3 seconds')",3000);

//To abort the interval you can use this:

How to make a text box have rounded corners?

You could use CSS to do that, but it wouldn't be supported in IE8-. You can use some site like to come up with actual CSS you'd use, which would look something like this (again, depending on how many browsers you're trying to support):

-webkit-border-radius: 5px;
-moz-border-radius: 5px;
border-radius: 5px;

Where can I download IntelliJ IDEA Color Schemes?

Please note there are two very nice color schemes by default in IDEA 10.

The one that is included is named Railcasts. It is included with the Ruby plugin (free official plugin, install via plugin manager).

Railcasts IDEA 10 color scheme

How to read a text-file resource into Java unit test?

You can try doing:

String myResource = IOUtils.toString(this.getClass().getResourceAsStream("yourfile.xml")).replace("\n","");

Detect if checkbox is checked or unchecked in Angular.js ng-change event

You could just use the bound ng-model (answers[item.questID]) value itself in your ng-change method to detect if it has been checked or not.


<input type="checkbox" ng-model="answers[item.questID]" 
     ng-change="stateChanged(item.questID)" /> <!-- Pass the specific id -->


$scope.stateChanged = function (qId) {
   if($scope.answers[qId]){ //If it is checked

Replace a string in a file with nodejs

On Linux or Mac, keep is simple and just use sed with the shell. No external libraries required. The following code works on Linux.

const shell = require('child_process').execSync
shell(`sed -i "s!oldString!newString!g" ./yourFile.js`)

The sed syntax is a little different on Mac. I can't test it right now, but I believe you just need to add an empty string after the "-i":

const shell = require('child_process').execSync
shell(`sed -i "" "s!oldString!newString!g" ./yourFile.js`)

The "g" after the final "!" makes sed replace all instances on a line. Remove it, and only the first occurrence per line will be replaced.

Convert int to a bit array in .NET

To convert the int 'x'

int x = 3;

One way, by manipulation on the int :

string s = Convert.ToString(x, 2); //Convert to binary in a string

int[] bits= s.PadLeft(8, '0') // Add 0's from left
             .Select(c => int.Parse(c.ToString())) // convert each char to int
             .ToArray(); // Convert IEnumerable from select to Array

Alternatively, by using the BitArray class-

BitArray b = new BitArray(new byte[] { x });
int[] bits = b.Cast<bool>().Select(bit => bit ? 1 : 0).ToArray();

Removing whitespace between HTML elements when using line breaks

After way too much research, trial and error I found a way that seems to works fine and doesn't require to manually re-set the font size manually on the children elements, allowing me to have a standardized em font size across the whole doc.

In Firefox this is fairly simple, just set word-spacing: -1em on the parent element. For some reason, Chrome ignore this (and as far as I tested, it ignores the word spacing regardless of the value). So besides this I add letter-spacing: -.31em to the parent and letter-spacing: normal to the children. This fraction of an em is the size of the space ONLY IF your em size is standardized. Firefox, in turn, ignores negative values for letter-spacing, so it won't add it to the word spacing.

I tested this on Firefox 13 (win/ubuntu, 14 on android), Google Chrome 20 (win/ubuntu), Android Browser on ICS 4.0.4 and IE 9. And I'm tempted to say this may also work on Safari, but I don't really know...

Here's a demo

Spring Boot and how to configure connection details to MongoDB?

Just to quote Boot Docs:

You can set property to change the url, or alternatively specify a host/port. For example, you might declare the following in your

All available options for prefix are fields of MongoProperties:

private String host;

private int port = DBPort.PORT;

private String uri = "mongodb://localhost/test";

private String database;

private String gridFsDatabase;

private String username;

private char[] password;

Detecting EOF in C

EOF is a constant in C. You are not checking the actual file for EOF. You need to do something like this


Here is the documentation to feof. You can also check the return value of scanf. It returns the number of successfully converted items, or EOF if it reaches the end of the file.

Multiplying across in a numpy array

I've compared the different options for speed and found that – much to my surprise – all options (except diag) are equally fast. I personally use

A * b[:, None]

(or (A.T * b).T) because it's short.

enter image description here

Code to reproduce the plot:

import numpy
import perfplot

def newaxis(data):
    A, b = data
    return A * b[:, numpy.newaxis]

def none(data):
    A, b = data
    return A * b[:, None]

def double_transpose(data):
    A, b = data
    return (A.T * b).T

def double_transpose_contiguous(data):
    A, b = data
    return numpy.ascontiguousarray((A.T * b).T)

def diag_dot(data):
    A, b = data
    return, A)

def einsum(data):
    A, b = data
    return numpy.einsum("ij,i->ij", A, b)
    setup=lambda n: (numpy.random.rand(n, n), numpy.random.rand(n)),
    n_range=[2 ** k for k in range(13)],
    xlabel="len(A), len(b)",

Why use the params keyword?

Adding params keyword itself shows that you can pass multiple number of parameters while calling that method which is not possible without using it. To be more specific:

static public int addTwoEach(params int[] args)
    int sum = 0;

    foreach (var item in args)
        sum += item + 2;

    return sum;

When you will call above method you can call it by any of the following ways:

  1. addTwoEach()
  2. addTwoEach(1)
  3. addTwoEach(new int[]{ 1, 2, 3, 4 })

But when you will remove params keyword only third way of the above given ways will work fine. For 1st and 2nd case you will get an error.

How to convert HTML to PDF using iText

You can do it with the HTMLWorker class (deprecated) like this:

import com.itextpdf.text.html.simpleparser.HTMLWorker;
try {
    String k = "<html><body> This is my Project </body></html>";
    OutputStream file = new FileOutputStream(new File("C:\\Test.pdf"));
    Document document = new Document();
    PdfWriter.getInstance(document, file);;
    HTMLWorker htmlWorker = new HTMLWorker(document);
    htmlWorker.parse(new StringReader(k));
} catch (Exception e) {

or using the XMLWorker, (download from this jar) using this code:

import com.itextpdf.tool.xml.XMLWorkerHelper;
try {
    String k = "<html><body> This is my Project </body></html>";
    OutputStream file = new FileOutputStream(new File("C:\\Test.pdf"));
    Document document = new Document();
    PdfWriter writer = PdfWriter.getInstance(document, file);;
    InputStream is = new ByteArrayInputStream(k.getBytes());
    XMLWorkerHelper.getInstance().parseXHtml(writer, document, is);
} catch (Exception e) {

Using SimpleXML to create an XML object from scratch

Please see my answer here. As points out, it is possible to do this with SimpleXML, but the DOM extension would be the better and more flexible way. Additionally there is a third way: using XMLWriter. It's much more simple to use than the DOM and therefore it's my preferred way of writing XML documents from scratch.

$w=new XMLWriter();
    $w->writeAttribute("ah", "OK");
    $w->text('Wow, it works!');
echo htmlentities($w->outputMemory(true));

By the way: DOM stands for Document Object Model; this is the standardized API into XML documents.

How to get the absolute coordinates of a view

You can get a View's coordinates using getLocationOnScreen() or getLocationInWindow()

Afterwards, x and y should be the top-left corner of the view. If your root layout is smaller than the screen (like in a Dialog), using getLocationInWindow will be relative to its container, not the entire screen.

Java Solution

int[] point = new int[2];
view.getLocationOnScreen(point); // or getLocationInWindow(point)
int x = point[0];
int y = point[1];

NOTE: If value is always 0, you are likely changing the view immediately before requesting location.

To ensure view has had a chance to update, run your location request after the View's new layout has been calculated by using -> {
    // Values should no longer be 0
    int[] point = new int[2];
    view.getLocationOnScreen(point); // or getLocationInWindow(point)
    int x = point[0];
    int y = point[1];


Kotlin Solution

val point = IntArray(2)
view.getLocationOnScreen(point) // or getLocationInWindow(point)
val (x, y) = point

NOTE: If value is always 0, you are likely changing the view immediately before requesting location.

To ensure view has had a chance to update, run your location request after the View's new layout has been calculated by using {
    // Values should no longer be 0
    val point = IntArray(2)
    view.getLocationOnScreen(point) // or getLocationInWindow(point)
    val (x, y) = point

I recommend creating an extension function for handling this:

// To use, call:
val (x, y) = view.screenLocation

val View.screenLocation get(): IntArray {
    val point = IntArray(2)
    return point

And if you require reliability, also add:

view.screenLocationSafe { x, y -> Log.d("", "Use $x and $y here") }

fun View.screenLocationSafe(callback: (Int, Int) -> Unit) {
    post {
        val (x, y) = screenLocation
        callback(x, y)

global variable for all controller and views

In file - \vendor\autoload.php, define your gobals variable as follows, should be in the topmost line.

$global_variable = "Some value";//the global variable

Access that global variable anywhere as :-


Enjoy :)

HikariCP - connection is not available

I managed to fix it finally. The problem is not related to HikariCP. The problem persisted because of some complex methods in REST controllers executing multiple changes in DB through JPA repositories. For some reasons calls to these interfaces resulted in a growing number of "freezed" active connections, exhausting the pool. Either annotating these methods as @Transactional or enveloping all the logic in a single call to transactional service method seem to solve the problem.

CSS text-align not working

Change the rule on your <a> element from:

.navigation ul a {
    color: #000;
    display: block;
    padding: 0 65px 0 0;
    text-decoration: none;


.navigation ul a {
    color: #000;
    display: block;
    padding: 0 65px 0 0;
    text-decoration: none;

Just add two new rules (width:100%; and text-align:center;). You need to make the anchor expand to take up the full width of the list item and then text-align center it.

jsFiddle example

How to add \newpage in Rmarkdown in a smart way?

Simply \newpage or \pagebreak will work, e.g.

hello world
```{r, echo=FALSE}
```{r, echo=FALSE}

This solution assumes you are knitting PDF. For HTML, you can achieve a similar effect by adding a tag <P style="page-break-before: always">. Note that you likely won't see a page break in your browser (HTMLs don't have pages per se), but the printing layout will have it.

How to represent empty char in Java Character class

I was looking for this. Simply set the char c = 0; and it works perfectly. Try it.

For example, if you are trying to remove duplicate characters from a String , one way would be to convert the string to char array and store in a hashset of characters which would automatically prevent duplicates.

Another way, however, will be to convert the string to a char array, use two for-loops and compare each character with the rest of the string/char array (a Big O on N^2 activity), then for each duplicate found just set that char to 0..

...and use new String(char[]) to convert the resulting char array to string and then sysout to print (this is all java btw). you will observe all chars set to zero are simply not there and all duplicates are gone. long post, but just wanted to give you an example.

so yes set char c = 0; or if for char array, set cArray[i]=0 for that specific duplicate character and you will have removed it.

Returning a value from callback function in Node.js

I am facing small trouble in returning a value from callback function in Node.js

This is not a "small trouble", it is actually impossible to "return" a value in the traditional sense from an asynchronous function.

Since you cannot "return the value" you must call the function that will need the value once you have it. @display_name already answered your question, but I just wanted to point out that the return in doCall is not returning the value in the traditional way. You could write doCall as follow:

function doCall(urlToCall, callback) {
    urllib.request(urlToCall, { wd: 'nodejs' }, function (err, data, response) {                              
        var statusCode = response.statusCode;
        finalData = getResponseJson(statusCode, data.toString());
        // call the function that needs the value
        // we are done

Line callback(finalData); is what calls the function that needs the value that you got from the async function. But be aware that the return statement is used to indicate that the function ends here, but it does not mean that the value is returned to the caller (the caller already moved on.)

Apache shutdown unexpectedly

i think the error is here

[pid 5384:tid 240] AH01909: RSA certificate configured for does NOT include an ID which matches the server name

or there is another app are using the port 80 try restarting your computer and only opening apache and see what happens

or try on reinstalling apache or using Ampps

Console.log not working at all

Click on the restore button. console.log will start to work.

enter image description here

How to trigger checkbox click event even if it's checked through Javascript code?


    var checked = $(this).is(":checked");
      alert('Checked Successfully');


Attempted to read or write protected memory. This is often an indication that other memory is corrupt

In some cases, this might happen when:

obj = new obj();
obj.Dispose();  // <-----------------    Incorrect disposal causes it

Different color for each bar in a bar chart; ChartJS

If you know which colors you want, you can specify color properties in an array, like so:

    backgroundColor: [
    'rgba(75, 192, 192, 1)',
    borderColor: [
    'rgba(75, 192, 192, 1)',

mysql delete under safe mode

Turning off safe mode in Mysql workbench

Edit menu => Preferences => SQL Editor : Other section: click on "Safe updates" ... to uncheck option

Workbench Preferences

What is the difference between parseInt(string) and Number(string) in JavaScript?

The first one takes two parameters:

parseInt(string, radix)

The radix parameter is used to specify which numeral system to be used, for example, a radix of 16 (hexadecimal) indicates that the number in the string should be parsed from a hexadecimal number to a decimal number.

If the radix parameter is omitted, JavaScript assumes the following:

  • If the string begins with "0x", the
    radix is 16 (hexadecimal)
  • If the string begins with "0", the radix is 8 (octal). This feature
    is deprecated
  • If the string begins with any other value, the radix is 10 (decimal)

The other function you mentioned takes only one parameter:


The Number() function converts the object argument to a number that represents the object's value.

If the value cannot be converted to a legal number, NaN is returned.

How to style HTML5 range input to have different color before and after slider?

Yes, it is possible. Though I wouldn't recommend it because input range is not really supported properly by all browsers because is an new element added in HTML5 and HTML5 is only a draft (and will be for long) so going as far as to styling it is perhaps not the best choice.

Also, you'll need a bit of JavaScript too. I took the liberty of using jQuery library for this, for simplicity purposes.

Here you go:

Angularjs Template Default Value if Binding Null / Undefined (With Filter)

In your cshtml,

<tr ng-repeat="value in Results">                
 <td>{{value.FileReceivedOn | mydate | date : 'dd-MM-yyyy'}} </td>

In Your JS File, maybe app.js,

Outside of app.controller, add the below filter.

Here the "mydate" is the function which you are calling for parsing the date. Here the "app" is the variable which contains the angular.module

app.filter("mydate", function () {
    var re = /\/Date\(([0-9]*)\)\//;
    return function (x) {
        var m = x.match(re);
        if (m) return new Date(parseInt(m[1]));
        else return null;

How to create a batch file to run cmd as administrator

Press Ctrl+Shift and double-click a shortcut to run as an elevated process.

Works from the start menu as well.

Dropdown select with images

I am a little to late on this, but you can do this using a simple bootstrap drop down and then do your code on select change event in any language or framework. (This is just a very basic solution, for other people like me who are just starting out and looking for a solution for a small simple project.)

<div class="dropdown">
    <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown" aria-haspopup="true" aria-expanded="true">
        Select Image
        <span class="caret"></span>
    <ul class="dropdown-menu" aria-labelledby="dropdownMenu1">
        <li> <a style="background-image: url(../Content/Images/Backgrounds/background.png);height:100px;width:300px" class="img-thumbnail" href=""> </a></li>
        <li role="separator" class="divider"></li>
        <li> <a style="background-image: url(../Content/Images/Backgrounds/background.png);height:100px;width:300px" class="img-thumbnail" href=""> </a></li>

Javascript date.getYear() returns 111 in 2011?

From what I've read on Mozilla's JS pages, getYear is deprecated. As pointed out many times, getFullYear() is the way to go. If you're really wanting to use getYear() add 1900 to it.

var now = new Date(),
    year = now.getYear() + 1900;

The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead

  1. Why is this happening?

    The entire ext/mysql PHP extension, which provides all functions named with the prefix mysql_, was officially deprecated in PHP v5.5.0 and removed in PHP v7.

    It was originally introduced in PHP v2.0 (November 1997) for MySQL v3.20, and no new features have been added since 2006. Coupled with the lack of new features are difficulties in maintaining such old code amidst complex security vulnerabilities.

    The manual has contained warnings against its use in new code since June 2011.

  2. How can I fix it?

    As the error message suggests, there are two other MySQL extensions that you can consider: MySQLi and PDO_MySQL, either of which can be used instead of ext/mysql. Both have been in PHP core since v5.0, so if you're using a version that is throwing these deprecation errors then you can almost certainly just start using them right away—i.e. without any installation effort.

    They differ slightly, but offer a number of advantages over the old extension including API support for transactions, stored procedures and prepared statements (thereby providing the best way to defeat SQL injection attacks). PHP developer Ulf Wendel has written a thorough comparison of the features. has an excellent tutorial on migrating from ext/mysql to PDO.

  3. I understand that it's possible to suppress deprecation errors by setting error_reporting in php.ini to exclude E_DEPRECATED:

    error_reporting = E_ALL ^ E_DEPRECATED

    What will happen if I do that?

    Yes, it is possible to suppress such error messages and continue using the old ext/mysql extension for the time being. But you really shouldn't do this—this is a final warning from the developers that the extension may not be bundled with future versions of PHP (indeed, as already mentioned, it has been removed from PHP v7). Instead, you should take this opportunity to migrate your application now, before it's too late.

    Note also that this technique will suppress all E_DEPRECATED messages, not just those to do with the ext/mysql extension: therefore you may be unaware of other upcoming changes to PHP that would affect your application code. It is, of course, possible to only suppress errors that arise on the expression at issue by using PHP's error control operator—i.e. prepending the relevant line with @—however this will suppress all errors raised by that expression, not just E_DEPRECATED ones.

What should you do?

  • You are starting a new project.

    There is absolutely no reason to use ext/mysql—choose one of the other, more modern, extensions instead and reap the rewards of the benefits they offer.

  • You have (your own) legacy codebase that currently depends upon ext/mysql.

    It would be wise to perform regression testing: you really shouldn't be changing anything (especially upgrading PHP) until you have identified all of the potential areas of impact, planned around each of them and then thoroughly tested your solution in a staging environment.

    • Following good coding practice, your application was developed in a loosely integrated/modular fashion and the database access methods are all self-contained in one place that can easily be swapped out for one of the new extensions.

      Spend half an hour rewriting this module to use one of the other, more modern, extensions; test thoroughly. You can later introduce further refinements to reap the rewards of the benefits they offer.

    • The database access methods are scattered all over the place and cannot easily be swapped out for one of the new extensions.

      Consider whether you really need to upgrade to PHP v5.5 at this time.

      You should begin planning to replace ext/mysql with one of the other, more modern, extensions in order that you can reap the rewards of the benefits they offer; you might also use it as an opportunity to refactor your database access methods into a more modular structure.

      However, if you have an urgent need to upgrade PHP right away, you might consider suppressing deprecation errors for the time being: but first be sure to identify any other deprecation errors that are also being thrown.

  • You are using a third party project that depends upon ext/mysql.

    Consider whether you really need to upgrade to PHP v5.5 at this time.

    Check whether the developer has released any fixes, workarounds or guidance in relation to this specific issue; or, if not, pressure them to do so by bringing this matter to their attention. If you have an urgent need to upgrade PHP right away, you might consider suppressing deprecation errors for the time being: but first be sure to identify any other deprecation errors that are also being thrown.

    It is absolutely essential to perform regression testing.

How to add a boolean datatype column to an existing table in sql?

In phpmyadmin, If you need to add a boolean datatype column to an existing table with default value true:

   isAvailable boolean default true;

One-line list comprehension: if-else variants

Just another solution, hope some one may like it :

Using: [False, True][Expression]

>>> map(lambda x: [x*100, x][x % 2 != 0], range(1,10))
[1, 200, 3, 400, 5, 600, 7, 800, 9]

How do I clear all variables in the middle of a Python script?

In Spyder one can configure the IPython console for each Python file to clear all variables before each execution in the Menu Run -> Configuration -> General settings -> Remove all variables before execution.

How do I run a class in a WAR from the command line?

the best way if you use Spring Boot is :

1/ Create a ServletInitializer extends SpringBootServletInitializer Class . With method configure which run your Application Class

2/ Generate always a maven install WAR file

3/ With this artefact you can even :

    . start application from war file with java -jar file.war

    . put your war file in your favorite Web App server (like tomcat, ...)

What is com.sun.proxy.$Proxy

  1. Proxies are classes that are created and loaded at runtime. There is no source code for these classes. I know that you are wondering how you can make them do something if there is no code for them. The answer is that when you create them, you specify an object that implements InvocationHandler, which defines a method that is invoked when a proxy method is invoked.

  2. You create them by using the call

    Proxy.newProxyInstance(classLoader, interfaces, invocationHandler)

    The arguments are:

    1. classLoader. Once the class is generated, it is loaded with this class loader.
    2. interfaces. An array of class objects that must all be interfaces. The resulting proxy implements all of these interfaces.
    3. invocationHandler. This is how your proxy knows what to do when a method is invoked. It is an object that implements InvocationHandler. When a method from any of the supported interfaces, or hashCode, equals, or toString, is invoked, the method invoke is invoked on the handler, passing the Method object for the method to be invoked and the arguments passed.

    For more on this, see the documentation for the Proxy class.

  3. Every implementation of a JVM after version 1.3 must support these. They are loaded into the internal data structures of the JVM in an implementation-specific way, but it is guaranteed to work.

How to make function decorators and chain them together?

If you are not into long explanations, see Paolo Bergantino’s answer.

Decorator Basics

Python’s functions are objects

To understand decorators, you must first understand that functions are objects in Python. This has important consequences. Let’s see why with a simple example :

def shout(word="yes"):
    return word.capitalize()+"!"

# outputs : 'Yes!'

# As an object, you can assign the function to a variable like any other object 
scream = shout

# Notice we don't use parentheses: we are not calling the function,
# we are putting the function "shout" into the variable "scream".
# It means you can then call "shout" from "scream":

# outputs : 'Yes!'

# More than that, it means you can remove the old name 'shout',
# and the function will still be accessible from 'scream'

del shout
except NameError as e:
    #outputs: "name 'shout' is not defined"

# outputs: 'Yes!'

Keep this in mind. We’ll circle back to it shortly.

Another interesting property of Python functions is they can be defined inside another function!

def talk():

    # You can define a function on the fly in "talk" ...
    def whisper(word="yes"):
        return word.lower()+"..."

    # ... and use it right away!

# You call "talk", that defines "whisper" EVERY TIME you call it, then
# "whisper" is called in "talk". 
# outputs: 
# "yes..."

# But "whisper" DOES NOT EXIST outside "talk":

except NameError as e:
    #outputs : "name 'whisper' is not defined"*
    #Python's functions are objects

Functions references

Okay, still here? Now the fun part...

You’ve seen that functions are objects. Therefore, functions:

  • can be assigned to a variable
  • can be defined in another function

That means that a function can return another function.

def getTalk(kind="shout"):

    # We define functions on the fly
    def shout(word="yes"):
        return word.capitalize()+"!"

    def whisper(word="yes") :
        return word.lower()+"...";

    # Then we return one of them
    if kind == "shout":
        # We don't use "()", we are not calling the function,
        # we are returning the function object
        return shout  
        return whisper

# How do you use this strange beast?

# Get the function and assign it to a variable
talk = getTalk()      

# You can see that "talk" is here a function object:
#outputs : <function shout at 0xb7ea817c>

# The object is the one returned by the function:
#outputs : Yes!

# And you can even use it directly if you feel wild:
#outputs : yes...

There’s more!

If you can return a function, you can pass one as a parameter:

def doSomethingBefore(func): 
    print("I do something before then I call the function you gave me")

#I do something before then I call the function you gave me

Well, you just have everything needed to understand decorators. You see, decorators are “wrappers”, which means that they let you execute code before and after the function they decorate without modifying the function itself.

Handcrafted decorators

How you’d do it manually:

# A decorator is a function that expects ANOTHER function as parameter
def my_shiny_new_decorator(a_function_to_decorate):

    # Inside, the decorator defines a function on the fly: the wrapper.
    # This function is going to be wrapped around the original function
    # so it can execute code before and after it.
    def the_wrapper_around_the_original_function():

        # Put here the code you want to be executed BEFORE the original function is called
        print("Before the function runs")

        # Call the function here (using parentheses)

        # Put here the code you want to be executed AFTER the original function is called
        print("After the function runs")

    # At this point, "a_function_to_decorate" HAS NEVER BEEN EXECUTED.
    # We return the wrapper function we have just created.
    # The wrapper contains the function and the code to execute before and after. It’s ready to use!
    return the_wrapper_around_the_original_function

# Now imagine you create a function you don't want to ever touch again.
def a_stand_alone_function():
    print("I am a stand alone function, don't you dare modify me")

#outputs: I am a stand alone function, don't you dare modify me

# Well, you can decorate it to extend its behavior.
# Just pass it to the decorator, it will wrap it dynamically in 
# any code you want and return you a new function ready to be used:

a_stand_alone_function_decorated = my_shiny_new_decorator(a_stand_alone_function)
#Before the function runs
#I am a stand alone function, don't you dare modify me
#After the function runs

Now, you probably want that every time you call a_stand_alone_function, a_stand_alone_function_decorated is called instead. That’s easy, just overwrite a_stand_alone_function with the function returned by my_shiny_new_decorator:

a_stand_alone_function = my_shiny_new_decorator(a_stand_alone_function)
#Before the function runs
#I am a stand alone function, don't you dare modify me
#After the function runs

# That’s EXACTLY what decorators do!

Decorators demystified

The previous example, using the decorator syntax:

def another_stand_alone_function():
    print("Leave me alone")

#Before the function runs
#Leave me alone
#After the function runs

Yes, that’s all, it’s that simple. @decorator is just a shortcut to:

another_stand_alone_function = my_shiny_new_decorator(another_stand_alone_function)

Decorators are just a pythonic variant of the decorator design pattern. There are several classic design patterns embedded in Python to ease development (like iterators).

Of course, you can accumulate decorators:

def bread(func):
    def wrapper():
    return wrapper

def ingredients(func):
    def wrapper():
    return wrapper

def sandwich(food="--ham--"):

#outputs: --ham--
sandwich = bread(ingredients(sandwich))
# #tomatoes#
# --ham--
# ~salad~

Using the Python decorator syntax:

def sandwich(food="--ham--"):

# #tomatoes#
# --ham--
# ~salad~

The order you set the decorators MATTERS:

def strange_sandwich(food="--ham--"):

# --ham--
# ~salad~

Now: to answer the question...

As a conclusion, you can easily see how to answer the question:

# The decorator to make it bold
def makebold(fn):
    # The new function the decorator returns
    def wrapper():
        # Insertion of some code before and after
        return "<b>" + fn() + "</b>"
    return wrapper

# The decorator to make it italic
def makeitalic(fn):
    # The new function the decorator returns
    def wrapper():
        # Insertion of some code before and after
        return "<i>" + fn() + "</i>"
    return wrapper

def say():
    return "hello"

#outputs: <b><i>hello</i></b>

# This is the exact equivalent to 
def say():
    return "hello"
say = makebold(makeitalic(say))

#outputs: <b><i>hello</i></b>

You can now just leave happy, or burn your brain a little bit more and see advanced uses of decorators.

Taking decorators to the next level

Passing arguments to the decorated function

# It’s not black magic, you just have to let the wrapper 
# pass the argument:

def a_decorator_passing_arguments(function_to_decorate):
    def a_wrapper_accepting_arguments(arg1, arg2):
        print("I got args! Look: {0}, {1}".format(arg1, arg2))
        function_to_decorate(arg1, arg2)
    return a_wrapper_accepting_arguments

# Since when you are calling the function returned by the decorator, you are
# calling the wrapper, passing arguments to the wrapper will let it pass them to 
# the decorated function

def print_full_name(first_name, last_name):
    print("My name is {0} {1}".format(first_name, last_name))

print_full_name("Peter", "Venkman")
# outputs:
#I got args! Look: Peter Venkman
#My name is Peter Venkman

Decorating methods

One nifty thing about Python is that methods and functions are really the same. The only difference is that methods expect that their first argument is a reference to the current object (self).

That means you can build a decorator for methods the same way! Just remember to take self into consideration:

def method_friendly_decorator(method_to_decorate):
    def wrapper(self, lie):
        lie = lie - 3 # very friendly, decrease age even more :-)
        return method_to_decorate(self, lie)
    return wrapper

class Lucy(object):

    def __init__(self):
        self.age = 32

    def sayYourAge(self, lie):
        print("I am {0}, what did you think?".format(self.age + lie))

l = Lucy()
#outputs: I am 26, what did you think?

If you’re making general-purpose decorator--one you’ll apply to any function or method, no matter its arguments--then just use *args, **kwargs:

def a_decorator_passing_arbitrary_arguments(function_to_decorate):
    # The wrapper accepts any arguments
    def a_wrapper_accepting_arbitrary_arguments(*args, **kwargs):
        print("Do I have args?:")
        # Then you unpack the arguments, here *args, **kwargs
        # If you are not familiar with unpacking, check:
        function_to_decorate(*args, **kwargs)
    return a_wrapper_accepting_arbitrary_arguments

def function_with_no_argument():
    print("Python is cool, no argument here.")

#Do I have args?:
#Python is cool, no argument here.

def function_with_arguments(a, b, c):
    print(a, b, c)

#Do I have args?:
#(1, 2, 3)
#1 2 3 

def function_with_named_arguments(a, b, c, platypus="Why not ?"):
    print("Do {0}, {1} and {2} like platypus? {3}".format(a, b, c, platypus))

function_with_named_arguments("Bill", "Linus", "Steve", platypus="Indeed!")
#Do I have args ? :
#('Bill', 'Linus', 'Steve')
#{'platypus': 'Indeed!'}
#Do Bill, Linus and Steve like platypus? Indeed!

class Mary(object):

    def __init__(self):
        self.age = 31

    def sayYourAge(self, lie=-3): # You can now add a default value
        print("I am {0}, what did you think?".format(self.age + lie))

m = Mary()
# Do I have args?:
#(<__main__.Mary object at 0xb7d303ac>,)
#I am 28, what did you think?

Passing arguments to the decorator

Great, now what would you say about passing arguments to the decorator itself?

This can get somewhat twisted, since a decorator must accept a function as an argument. Therefore, you cannot pass the decorated function’s arguments directly to the decorator.

Before rushing to the solution, let’s write a little reminder:

# Decorators are ORDINARY functions
def my_decorator(func):
    print("I am an ordinary function")
    def wrapper():
        print("I am function returned by the decorator")
    return wrapper

# Therefore, you can call it without any "@"

def lazy_function():

decorated_function = my_decorator(lazy_function)
#outputs: I am an ordinary function

# It outputs "I am an ordinary function", because that’s just what you do:
# calling a function. Nothing magic.

def lazy_function():

#outputs: I am an ordinary function

It’s exactly the same. "my_decorator" is called. So when you @my_decorator, you are telling Python to call the function 'labelled by the variable "my_decorator"'.

This is important! The label you give can point directly to the decorator—or not.

Let’s get evil. ?

def decorator_maker():

    print("I make decorators! I am executed only once: "
          "when you make me create a decorator.")

    def my_decorator(func):

        print("I am a decorator! I am executed only when you decorate a function.")

        def wrapped():
            print("I am the wrapper around the decorated function. "
                  "I am called when you call the decorated function. "
                  "As the wrapper, I return the RESULT of the decorated function.")
            return func()

        print("As the decorator, I return the wrapped function.")

        return wrapped

    print("As a decorator maker, I return a decorator")
    return my_decorator

# Let’s create a decorator. It’s just a new function after all.
new_decorator = decorator_maker()       
#I make decorators! I am executed only once: when you make me create a decorator.
#As a decorator maker, I return a decorator

# Then we decorate the function

def decorated_function():
    print("I am the decorated function.")

decorated_function = new_decorator(decorated_function)
#I am a decorator! I am executed only when you decorate a function.
#As the decorator, I return the wrapped function

# Let’s call the function:
#I am the wrapper around the decorated function. I am called when you call the decorated function.
#As the wrapper, I return the RESULT of the decorated function.
#I am the decorated function.

No surprise here.

Let’s do EXACTLY the same thing, but skip all the pesky intermediate variables:

def decorated_function():
    print("I am the decorated function.")
decorated_function = decorator_maker()(decorated_function)
#I make decorators! I am executed only once: when you make me create a decorator.
#As a decorator maker, I return a decorator
#I am a decorator! I am executed only when you decorate a function.
#As the decorator, I return the wrapped function.

# Finally:
#I am the wrapper around the decorated function. I am called when you call the decorated function.
#As the wrapper, I return the RESULT of the decorated function.
#I am the decorated function.

Let’s make it even shorter:

def decorated_function():
    print("I am the decorated function.")
#I make decorators! I am executed only once: when you make me create a decorator.
#As a decorator maker, I return a decorator
#I am a decorator! I am executed only when you decorate a function.
#As the decorator, I return the wrapped function.

#I am the wrapper around the decorated function. I am called when you call the decorated function.
#As the wrapper, I return the RESULT of the decorated function.
#I am the decorated function.

Hey, did you see that? We used a function call with the "@" syntax! :-)

So, back to decorators with arguments. If we can use functions to generate the decorator on the fly, we can pass arguments to that function, right?

def decorator_maker_with_arguments(decorator_arg1, decorator_arg2):

    print("I make decorators! And I accept arguments: {0}, {1}".format(decorator_arg1, decorator_arg2))

    def my_decorator(func):
        # The ability to pass arguments here is a gift from closures.
        # If you are not comfortable with closures, you can assume it’s ok,
        # or read:
        print("I am the decorator. Somehow you passed me arguments: {0}, {1}".format(decorator_arg1, decorator_arg2))

        # Don't confuse decorator arguments and function arguments!
        def wrapped(function_arg1, function_arg2) :
            print("I am the wrapper around the decorated function.\n"
                  "I can access all the variables\n"
                  "\t- from the decorator: {0} {1}\n"
                  "\t- from the function call: {2} {3}\n"
                  "Then I can pass them to the decorated function"
                  .format(decorator_arg1, decorator_arg2,
                          function_arg1, function_arg2))
            return func(function_arg1, function_arg2)

        return wrapped

    return my_decorator

@decorator_maker_with_arguments("Leonard", "Sheldon")
def decorated_function_with_arguments(function_arg1, function_arg2):
    print("I am the decorated function and only knows about my arguments: {0}"
           " {1}".format(function_arg1, function_arg2))

decorated_function_with_arguments("Rajesh", "Howard")
#I make decorators! And I accept arguments: Leonard Sheldon
#I am the decorator. Somehow you passed me arguments: Leonard Sheldon
#I am the wrapper around the decorated function. 
#I can access all the variables 
#   - from the decorator: Leonard Sheldon 
#   - from the function call: Rajesh Howard 
#Then I can pass them to the decorated function
#I am the decorated function and only knows about my arguments: Rajesh Howard

Here it is: a decorator with arguments. Arguments can be set as variable:

c1 = "Penny"
c2 = "Leslie"

@decorator_maker_with_arguments("Leonard", c1)
def decorated_function_with_arguments(function_arg1, function_arg2):
    print("I am the decorated function and only knows about my arguments:"
           " {0} {1}".format(function_arg1, function_arg2))

decorated_function_with_arguments(c2, "Howard")
#I make decorators! And I accept arguments: Leonard Penny
#I am the decorator. Somehow you passed me arguments: Leonard Penny
#I am the wrapper around the decorated function. 
#I can access all the variables 
#   - from the decorator: Leonard Penny 
#   - from the function call: Leslie Howard 
#Then I can pass them to the decorated function
#I am the decorated function and only know about my arguments: Leslie Howard

As you can see, you can pass arguments to the decorator like any function using this trick. You can even use *args, **kwargs if you wish. But remember decorators are called only once. Just when Python imports the script. You can't dynamically set the arguments afterwards. When you do "import x", the function is already decorated, so you can't change anything.

Let’s practice: decorating a decorator

Okay, as a bonus, I'll give you a snippet to make any decorator accept generically any argument. After all, in order to accept arguments, we created our decorator using another function.

We wrapped the decorator.

Anything else we saw recently that wrapped function?

Oh yes, decorators!

Let’s have some fun and write a decorator for the decorators:

def decorator_with_args(decorator_to_enhance):
    This function is supposed to be used as a decorator.
    It must decorate an other function, that is intended to be used as a decorator.
    Take a cup of coffee.
    It will allow any decorator to accept an arbitrary number of arguments,
    saving you the headache to remember how to do that every time.

    # We use the same trick we did to pass arguments
    def decorator_maker(*args, **kwargs):

        # We create on the fly a decorator that accepts only a function
        # but keeps the passed arguments from the maker.
        def decorator_wrapper(func):

            # We return the result of the original decorator, which, after all, 
            # IS JUST AN ORDINARY FUNCTION (which returns a function).
            # Only pitfall: the decorator must have this specific signature or it won't work:
            return decorator_to_enhance(func, *args, **kwargs)

        return decorator_wrapper

    return decorator_maker

It can be used as follows:

# You create the function you will use as a decorator. And stick a decorator on it :-)
# Don't forget, the signature is "decorator(func, *args, **kwargs)"
def decorated_decorator(func, *args, **kwargs): 
    def wrapper(function_arg1, function_arg2):
        print("Decorated with {0} {1}".format(args, kwargs))
        return func(function_arg1, function_arg2)
    return wrapper

# Then you decorate the functions you wish with your brand new decorated decorator.

@decorated_decorator(42, 404, 1024)
def decorated_function(function_arg1, function_arg2):
    print("Hello {0} {1}".format(function_arg1, function_arg2))

decorated_function("Universe and", "everything")
#Decorated with (42, 404, 1024) {}
#Hello Universe and everything

# Whoooot!

I know, the last time you had this feeling, it was after listening a guy saying: "before understanding recursion, you must first understand recursion". But now, don't you feel good about mastering this?

Best practices: decorators

  • Decorators were introduced in Python 2.4, so be sure your code will be run on >= 2.4.
  • Decorators slow down the function call. Keep that in mind.
  • You cannot un-decorate a function. (There are hacks to create decorators that can be removed, but nobody uses them.) So once a function is decorated, it’s decorated for all the code.
  • Decorators wrap functions, which can make them hard to debug. (This gets better from Python >= 2.5; see below.)

The functools module was introduced in Python 2.5. It includes the function functools.wraps(), which copies the name, module, and docstring of the decorated function to its wrapper.

(Fun fact: functools.wraps() is a decorator! ?)

# For debugging, the stacktrace prints you the function __name__
def foo():

#outputs: foo

# With a decorator, it gets messy    
def bar(func):
    def wrapper():
        return func()
    return wrapper

def foo():

#outputs: wrapper

# "functools" can help for that

import functools

def bar(func):
    # We say that "wrapper", is wrapping "func"
    # and the magic begins
    def wrapper():
        return func()
    return wrapper

def foo():

#outputs: foo

How can the decorators be useful?

Now the big question: What can I use decorators for?

Seem cool and powerful, but a practical example would be great. Well, there are 1000 possibilities. Classic uses are extending a function behavior from an external lib (you can't modify it), or for debugging (you don't want to modify it because it’s temporary).

You can use them to extend several functions in a DRY’s way, like so:

def benchmark(func):
    A decorator that prints the time a function takes
    to execute.
    import time
    def wrapper(*args, **kwargs):
        t = time.clock()
        res = func(*args, **kwargs)
        print("{0} {1}".format(func.__name__, time.clock()-t))
        return res
    return wrapper

def logging(func):
    A decorator that logs the activity of the script.
    (it actually just prints it, but it could be logging!)
    def wrapper(*args, **kwargs):
        res = func(*args, **kwargs)
        print("{0} {1} {2}".format(func.__name__, args, kwargs))
        return res
    return wrapper

def counter(func):
    A decorator that counts and prints the number of times a function has been executed
    def wrapper(*args, **kwargs):
        wrapper.count = wrapper.count + 1
        res = func(*args, **kwargs)
        print("{0} has been used: {1}x".format(func.__name__, wrapper.count))
        return res
    wrapper.count = 0
    return wrapper

def reverse_string(string):
    return str(reversed(string))

print(reverse_string("Able was I ere I saw Elba"))
print(reverse_string("A man, a plan, a canoe, pasta, heros, rajahs, a coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal: Panama!"))

#reverse_string ('Able was I ere I saw Elba',) {}
#wrapper 0.0
#wrapper has been used: 1x 
#ablE was I ere I saw elbA
#reverse_string ('A man, a plan, a canoe, pasta, heros, rajahs, a coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal: Panama!',) {}
#wrapper 0.0
#wrapper has been used: 2x
#!amanaP :lanac a ,noep a ,stah eros ,raj a ,hsac ,oloR a ,tur a ,mapS ,snip ,eperc a ,)lemac a ro( niaga gab ananab a ,gat a ,nat a ,gab ananab a ,gag a ,inoracam ,elacrep ,epins ,spam ,arutaroloc a ,shajar ,soreh ,atsap ,eonac a ,nalp a ,nam A

Of course the good thing with decorators is that you can use them right away on almost anything without rewriting. DRY, I said:

def get_random_futurama_quote():
    from urllib import urlopen
    result = urlopen("").read()
        value = result.split("<br><b><hr><br>")[1].split("<br><br><hr>")[0]
        return value.strip()
        return "No, I'm ... doesn't!"


#get_random_futurama_quote () {}
#wrapper 0.02
#wrapper has been used: 1x
#The laws of science be a harsh mistress.
#get_random_futurama_quote () {}
#wrapper 0.01
#wrapper has been used: 2x
#Curse you, merciful Poseidon!

Python itself provides several decorators: property, staticmethod, etc.

  • Django uses decorators to manage caching and view permissions.
  • Twisted to fake inlining asynchronous functions calls.

This really is a large playground.

How can I create a temp file with a specific extension with .NET?

public static string GetTempFileName(string extension)
  int attempt = 0;
  while (true)
    string fileName = Path.GetRandomFileName();
    fileName = Path.ChangeExtension(fileName, extension);
    fileName = Path.Combine(Path.GetTempPath(), fileName);

      using (new FileStream(fileName, FileMode.CreateNew)) { }
      return fileName;
    catch (IOException ex)
      if (++attempt == 10)
        throw new IOException("No unique temporary file name is available.", ex);

Note: this works like Path.GetTempFileName. An empty file is created to reserve the file name. It makes 10 attempts, in case of collisions generated by Path.GetRandomFileName();

Why doesn't JavaScript support multithreading?

I don't know the rationale for this decision, but I know that you can simulate some of the benefits of multi-threaded programming using setTimeout. You can give the illusion of multiple processes doing things at the same time, though in reality, everything happens in one thread.

Just have your function do a little bit of work, and then call something like:

setTimeout(function () {
    ... do the rest of the work...
}, 0);

And any other things that need doing (like UI updates, animated images, etc) will happen when they get a chance.

mysql - move rows from one table to another

The answer of Fabio is really good but it take a long execution time (as Trilarion already has written)

I have an other solution with faster execution.

set @N := (now());
INSERT INTO table2 select * from table1 where ts < date_sub(@N,INTERVAL 32 DAY);
DELETE FROM table1 WHERE ts < date_sub(@N,INTERVAL 32 DAY);

@N gets the Timestamp at the begin and is used for both commands. All is in a Transaction to be sure nobody is disturbing

#1273 - Unknown collation: 'utf8mb4_unicode_ci' cPanel

If you have already exported a .sql file, the best thing to do is to Find and Replace the following if you have them in your file:

  • utf8mb4_0900_ai_ci to utf8_unicode_ci
  • utf8mb4 to utf8
  • utf8_unicode_520_ci to utf8_unicode_ci

It will replace utf8mb4_unicode_ci to utf8_unicode_ci. Now you go to your phpMyAdmin cPanel and set the DB collation to utf8_unicode_ci through Operations > Collation.

If you are exporting to a .sql, it's better to change the format on how you're exporting the file. Check out Evster's anwer (it's in the same page as this)

Retrieve Button value with jQuery

if you want to get the value attribute (buttonValue) then I'd use:

<script type="text/javascript">
    $(document).ready(function() {
        $('.my_button').click(function() {

How to convert a selection to lowercase or uppercase in Sublime Text

For others needing a key binding:

{ "keys": ["ctrl+="], "command": "upper_case" },
{ "keys": ["ctrl+-"], "command": "lower_case" }

How to set cell spacing and UICollectionView - UICollectionViewFlowLayout size ratio?

For Swift 3 and XCode 8, this worked. Follow below steps to achieve this:-

        let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
        var width = UIScreen.main.bounds.width
        layout.sectionInset = UIEdgeInsets(top: 0, left: 5, bottom: 0, right: 5)
    width = width - 10
    layout.itemSize = CGSize(width: width / 2, height: width / 2)
        layout.minimumInteritemSpacing = 0
        layout.minimumLineSpacing = 0
        collectionView!.collectionViewLayout = layout

Pass a PHP array to a JavaScript function


In the following example $php_variable can be any PHP variable.

<script type="text/javascript">
    var obj = <?php echo json_encode($php_variable); ?>;

In your code, you could use like the following:

drawChart(600/50, <?php echo json_encode($day); ?>, ...)

In cases where you need to parse out an object from JSON-string (like in an AJAX request), the safe way is to use JSON.parse(..) like the below:

var s = "<JSON-String>";
var obj = JSON.parse(s);

How do I call one constructor from another in Java?

As everybody already have said, you use this(…), which is called an explicit constructor invocation.

However, keep in mind that within such an explicit constructor invocation statement you may not refer to

  • any instance variables or
  • any instance methods or
  • any inner classes declared in this class or any superclass, or
  • this or
  • super.

As stated in JLS (§

Which port(s) does XMPP use?

According to Wikipedia:

5222 TCP     XMPP client connection (RFC 6120)        Official  
5223 TCP     XMPP client connection over SSL          Unofficial
5269 TCP     XMPP server connection (RFC 6120)        Official
5298 TCP UDP XMPP JEP-0174: Link-Local Messaging /    Official
             XEP-0174: Serverless Messaging
8010 TCP     XMPP File transfers                      Unofficial    

The port numbers are defined in RFC 6120 § 14.7.

What is a View in Oracle?

regular view----->short name for a query,no additional space is used here

Materialised view---->similar to creating table whose data will refresh periodically based on data query used for creating the view

What is the difference between compileSdkVersion and targetSdkVersion?

compiledSdkVersion==> which version of SDK should compile your code to bytecode(it uses in development environment) point: it's better use last version of SDK.

minSdkVersion==> these item uses for installation of APK(it uses in production environment). For example:

if(client-sdk-version   <   min-sdk-versoin )

How to use LocalBroadcastManager?

An example of an Activity and a Service implementing a LocalBroadcastManager can be found in the developer docs. I personally found it very useful.

EDIT: The link has since then been removed from the site, but the data is the following:

Switching users inside Docker image to a non-root user

As a different approach to the other answer, instead of indicating the user upon image creation on the Dockerfile, you can do so via command-line on a particular container as a per-command basis.

With docker exec, use --user to specify which user account the interactive terminal will use (the container should be running and the user has to exist in the containerized system):

docker exec -it --user [username] [container] bash


Live-stream video from one android phone to another over WiFi

If you do not need the recording and playback functionality in your app, using off-the-shelf streaming app and player is a reasonable choice.

If you do need them to be in your app, however, you will have to look into MediaRecorder API (for the server/camera app) and MediaPlayer (for client/player app).

Quick sample code for the server:

// this is your network socket
ParcelFileDescriptor pfd = ParcelFileDescriptor.fromSocket(socket);
mCamera = getCameraInstance();
mMediaRecorder = new MediaRecorder();
// this is the unofficially supported MPEG2TS format, suitable for streaming (Android 3.0+)

On the player side it is a bit tricky, you could try this:

// this is your network socket, connected to the server
ParcelFileDescriptor pfd = ParcelFileDescriptor.fromSocket(socket);
mMediaPlayer = new MediaPlayer();

Unfortunately mediaplayer tends to not like this, so you have a couple of options: either (a) save data from socket to file and (after you have a bit of data) play with mediaplayer from file, or (b) make a tiny http proxy that runs locally and can accept mediaplayer's GET request, reply with HTTP headers, and then copy data from the remote server to it. For (a) you would create the mediaplayer with a file path or file url, for (b) give it a http url pointing to your proxy.

See also:

Stream live video from phone to phone using socket fd

MediaPlayer stutters at start of mp3 playback

How do I return clean JSON from a WCF Service?

Change the return type of your GetResults to be List<Person>.
Eliminate the code that you use to serialize the List to a json string - WCF does this for you automatically.

Using your definition for the Person class, this code works for me:

public List<Person> GetPlayers()
    List<Person> players = new List<Person>();
    players.Add(new  Person { FirstName="Peyton", LastName="Manning", Age=35 } );
    players.Add(new  Person { FirstName="Drew", LastName="Brees", Age=31 } );
    players.Add(new  Person { FirstName="Brett", LastName="Favre", Age=58 } );

    return players;



(All on one line)

I also used this attribute on the method:

[WebInvoke(Method = "GET",
           RequestFormat = WebMessageFormat.Json,
           ResponseFormat = WebMessageFormat.Json,
           UriTemplate = "players")]

WebInvoke with Method= "GET" is the same as WebGet, but since some of my methods are POST, I use all WebInvoke for consistency.

The UriTemplate sets the URL at which the method is available. So I can do a GET on http://myserver/myvdir/JsonService.svc/players and it just works.

Also check out IIRF or another URL rewriter to get rid of the .svc in the URI.

Transaction isolation levels relation with locks on table

I want to understand the lock each transaction isolation takes on the table

For example, you have 3 concurrent processes A, B and C. A starts a transaction, writes data and commit/rollback (depending on results). B just executes a SELECT statement to read data. C reads and updates data. All these process work on the same table T.

  • READ UNCOMMITTED - no lock on the table. You can read data in the table while writing on it. This means A writes data (uncommitted) and B can read this uncommitted data and use it (for any purpose). If A executes a rollback, B still has read the data and used it. This is the fastest but most insecure way to work with data since can lead to data holes in not physically related tables (yes, two tables can be logically but not physically related in real-world apps =\).
  • READ COMMITTED - lock on committed data. You can read the data that was only committed. This means A writes data and B can't read the data saved by A until A executes a commit. The problem here is that C can update data that was read and used on B and B client won't have the updated data.
  • REPEATABLE READ - lock on a block of SQL(which is selected by using select query). This means B reads the data under some condition i.e. WHERE aField > 10 AND aField < 20, A inserts data where aField value is between 10 and 20, then B reads the data again and get a different result.
  • SERIALIZABLE - lock on a full table(on which Select query is fired). This means, B reads the data and no other transaction can modify the data on the table. This is the most secure but slowest way to work with data. Also, since a simple read operation locks the table, this can lead to heavy problems on production: imagine that T table is an Invoice table, user X wants to know the invoices of the day and user Y wants to create a new invoice, so while X executes the read of the invoices, Y can't add a new invoice (and when it's about money, people get really mad, especially the bosses).

I want to understand where we define these isolation levels: only at JDBC/hibernate level or in DB also

Using JDBC, you define it using Connection#setTransactionIsolation.

Using Hibernate:

<property name="hibernate.connection.isolation">2</property>



Hibernate configuration is taken from here (sorry, it's in Spanish).

By the way, you can set the isolation level on RDBMS as well:

and on and on...

How can I pair socks from a pile efficiently?

When I sort socks, I do an approximate radix sort, dropping socks near other socks of the same colour/pattern type. Except in the case when I can see an exact match at/near the location I'm about to drop the sock I extract the pair at that point.

Almost all the other algorithms (including the top scoring answer by usr) sort, then remove pairs. I find that, as a human, it is better to minimize the number of socks being considered at one time.

I do this by:

  1. Picking a distinctive sock (whatever catches my eye first in the pile).
  2. Starting a radix sort from that conceptual location by pulling socks from the pile based on similarity to that one.
  3. Place the new sock near into the current pile, with a distance based on how different it is. If you find yourself putting the sock on top of another because it is identical, form the pair there, and remove them. This means that future comparisons take less effort to find the correct place.

This takes advantage of the human ability to fuzzy-match in O(1) time, which is somewhat equivalent to the establishment of a hash-map on a computing device.

By pulling the distinctive socks first, you leave space to "zoom" in on the features which are less distinctive, to begin with.

After eliminating the fluro coloured, the socks with stripes, and the three pairs of long socks, you might end up with mostly white socks roughly sorted by how worn they are.

At some point, the differences between socks are small enough that other people won't notice the difference, and any further matching effort is not needed.

SQLAlchemy: how to filter date field?

In fact, your query is right except for the typo: your filter is excluding all records: you should change the <= for >= and vice versa:

qry = DBSession.query(User).filter(
        and_(User.birthday <= '1988-01-17', User.birthday >= '1985-01-17'))
# or same:
qry = DBSession.query(User).filter(User.birthday <= '1988-01-17').\
        filter(User.birthday >= '1985-01-17')

Also you can use between:

qry = DBSession.query(User).filter(User.birthday.between('1985-01-17', '1988-01-17'))

Installing OpenCV on Windows 7 for Python 2.7

Installing OpenCV on Windows 7 for Python 2.7

How to print / echo environment variables?

These need to go as different commands e.g.:

NAME=sam; echo "$NAME"
NAME=sam && echo "$NAME"

The expansion $NAME to empty string is done by the shell earlier, before running echo, so at the time the NAME variable is passed to the echo command's environment, the expansion is already done (to null string).

To get the same result in one command:

NAME=sam printenv NAME

Oracle - Best SELECT statement for getting the difference in minutes between two DateTime columns?

By default, oracle date subtraction returns a result in # of days.

So just multiply by 24 to get # of hours, and again by 60 for # of minutes.


  round((second_date - first_date) * (60 * 24),2) as time_in_minutes
    to_date('01/01/2008 01:30:00 PM','mm/dd/yyyy hh:mi:ss am') as first_date
   ,to_date('01/06/2008 01:35:00 PM','mm/dd/yyyy HH:MI:SS AM') as second_date
  ) test_data

Capture iOS Simulator video for App Preview

As of today in 2019, Apple has made life much easier for low budget or one-man project developers like me. You can just use the terminal command from one of the above posts to record videos from the wanted device simulator. And then use iMovie's New App Preview feature.

xcrun /Applications/ io booted recordVideo

iMovie -> File -> New App Preview

How to split a file into equal parts, without breaking individual lines?

If you mean an equal number of lines, split has an option for this:

split --lines=75

If you need to know what that 75 should really be for N equal parts, its:

lines_per_part = int(total_lines + N - 1) / N

where total lines can be obtained with wc -l.

See the following script for an example:


# Configuration stuff


# Work out lines per file.

total_lines=$(wc -l <${fspec})
((lines_per_file = (total_lines + num_files - 1) / num_files))

# Split the actual file, maintaining lines.

split --lines=${lines_per_file} ${fspec} xyzzy.

# Debug information

echo "Total lines     = ${total_lines}"
echo "Lines  per file = ${lines_per_file}"    
wc -l xyzzy.*

This outputs:

Total lines     = 70
Lines  per file = 12
  12 xyzzy.aa
  12 xyzzy.ab
  70 total

More recent versions of split allow you to specify a number of CHUNKS with the -n/--number option. You can therefore use something like:

split --number=l/6 ${fspec} xyzzy.

(that's ell-slash-six, meaning lines, not one-slash-six).

That will give you roughly equal files in terms of size, with no mid-line splits.

I mention that last point because it doesn't give you roughly the same number of lines in each file, more the same number of characters.

So, if you have one 20-character line and 19 1-character lines (twenty lines in total) and split to five files, you most likely won't get four lines in every file.

Design Android EditText to show error message as described by google

reVerse's answer is great but it didn't point out how to remove the floating error tooltip kind of thing

You'll need edittext.setError(null) to remove that.
Also, as someone pointed out, you don't need TextInputLayout.setErrorEnabled(true)



        android:hint="Enter something" />


TextInputLayout til = (TextInputLayout) editText.getParent();
til.setError("Your input is not valid...");